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Old 04-06-2010, 08:57 AM   #1
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Rattling Noise Only at low rpm when transmission is in gear

I started having this strange sound a few days ago, or at least that is the first time I noticed it. It happens when I first go into gear at low rpm. It sounds like a heat shield rattling and is not related to a cold or hot engine. It's easy to hear when I am driving alongside a car, fence, etc and the sound reflects back. I checked everything I could get to so far underneath the car and nothing is loose, but it only does it when the engine is at low rpms in gear, nothing when you gently rev engine in neutral. Does anyone have any ideas? Driving, the engine seems to have plenty of power and idles fine.


Last edited by dennis; 04-06-2010 at 09:00 AM.
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Old 04-06-2010, 11:28 AM   #2
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What year/milage is your car? Have you replaced your front motor mount? If it is failing, the engine can move and various parts can come in contact with heat shielding.

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Old 04-06-2010, 11:32 AM   #3
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Also check the plastic under panel covering the body, not the engine. Where it bolts, you get cracks and breaks, just the right speed and it becomes noticeable.
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Old 04-06-2010, 11:36 AM   #4
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it's an '01 with 34k miles. I will check further underneath, but it sounds like a fluttering noise almost. And its only when the engine is is in low gear at higher rpms, like down a hill coasting in 3rd or in 2nd driving.
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Old 04-06-2010, 12:30 PM   #5
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I hope its not a typical porsche engine nightmare?! Like IMS bearing?
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Old 04-06-2010, 03:04 PM   #6
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Quote:
Originally Posted by dennis
I started having this strange sound a few days ago, or at least that is the first time I noticed it. It happens when I first go into gear at low rpm. It sounds like a heat shield rattling and is not related to a cold or hot engine. It's easy to hear when I am driving alongside a car, fence, etc and the sound reflects back. I checked everything I could get to so far underneath the car and nothing is loose, but it only does it when the engine is at low rpms in gear, nothing when you gently rev engine in neutral. Does anyone have any ideas? Driving, the engine seems to have plenty of power and idles fine.
I have a similar rattling sound at 32,000 miles in my 2001 Boxster. I only hear it when I take off in 1st gear from a stop, but not after I'm rolling beyond 20 mph (or at idle).
I suspected an exhaust leak. I believe I have traced it to a vertical split or crack in the right side of the stock exhaust system at least a foot before the right and left exhaust passages join. It has been a couple weeks since I looked at this under the car, but I will try to shoot a pic of the split and post tomorrow.

Because I expect a big bill from the dealership, I have not done anything about it yet.
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Old 04-06-2010, 07:06 PM   #7
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That's interesting. I could only hope that its an exhaust leak. Whils still expensive I'm sure, atleast it isn't a catastrophic engine issue.I am still skeptical my problem is same thing. Mine makes noise at 1st, 2nd,3rd and possibly 4th and 5th but only when it is torqued in that gear-like starting out or downshifting
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Old 04-06-2010, 07:21 PM   #8
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mine was rattling at low rpm and i thought it was the exhaust as well, I went to investigate today and both sides of the drive shaft were dangerously loose. 3 of the bolts had no threads in at all, and the other 5 were on thier way out as well.

Tightened those babies and the rattle is gone....

Mine's a 2000 S with 40k

Lucky, lucky me!


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Old 04-06-2010, 07:23 PM   #9
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Jack the car up and put it on jack stands in the back. Get on your back and get under the car, and bring a hammer with you.

The metal heat shields on the cats make the exact sound you all are describing.

Hit the living crap out of the loose heat shield to bend it a little and tighten it up. This will feel really good if you are as pissed off as I was with that rattle buzz noises at low speeds in low gears in alley ways or by fencing.

Then get the car back out on the road near a fence and you won't hear it any longer. You will feel the satisfaction of knowing you beat your Porsche with a hammer and that's exactly what it needed and what your mechanic would have done, but charged you for it.
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Old 04-06-2010, 08:23 PM   #10
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It all sounds like this is originating from the exhaust. Does anyone still think it may be engine internal?
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Old 04-07-2010, 07:00 AM   #11
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Quote:
Originally Posted by RandallNeighbour
Jack the car up and put it on jack stands in the back. Get on your back and get under the car, and bring a hammer with you.

The metal heat shields on the cats make the exact sound you all are describing.

Hit the living crap out of the loose heat shield to bend it a little and tighten it up. This will feel really good if you are as pissed off as I was with that rattle buzz noises at low speeds in low gears in alley ways or by fencing.

Then get the car back out on the road near a fence and you won't hear it any longer. You will feel the satisfaction of knowing you beat your Porsche with a hammer and that's exactly what it needed and what your mechanic would have done, but charged you for it.
I checked out what I thought was a crack in the exhaust system last night and took a photo of it. But after probing the "crack" with a screwdriver and high intensity light, I realized it was just a gap between where the bracket for the cat converter is welded to the converter and the endcap of the converter. This gap is much deeper on the right side than what is seen on the left side of the car.
In the attached pic, the bogus "crack" is denoted by arrow #1.



Randall,
Does my arrow #2 point to the metal heat shield you refer to? Or is it even visible in this photo? Thanks.
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Old 04-07-2010, 09:07 AM   #12
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I stand by my engine mount statement, both David and Dennis are at the mileage where you'd want to consider replacing. The engine not being properly centered will exacerbate exhaust rattles.
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Old 04-07-2010, 04:20 PM   #13
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OK. It seems unanimous- engine mount, leading to exhaust noise. Just a few questions: will this cause damage to drivetrain and how difficult is it to replace the mount? Should I replace all? Assuming I should.
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Old 04-08-2010, 04:58 AM   #14
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Can anyone recommend the best mount to buy? I have seen Wevo and Pedro's mount, but what is best as far as long lasting durability?
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Old 04-08-2010, 10:58 AM   #15
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It's usually only the front mount that needs to be replaced. It's not super difficult, just time consuming. You have to support the weight of the engine while you are doing it, so you need a jack that doesn't leak down, or an engine support bar. If you go the support bar route, it's helpful to have a second person to help install it, and adjust it while you are under the car. I tried to do it myself and dented my fender.

I have Pedro's Enthusiast mount. I think a lot of it depends on whether you want the car to be a smoother quieter daily driver, or more aggressive. You can feel engine vibration through the seat with Pedro's mount around 3,000 rpm. The stock Porsche mount is quieter, but probably won't last as long.

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Old 04-08-2010, 11:30 AM   #16
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Thnaks for the help here...I really appreciate it. I'll post back when I have it all fixed.
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Old 04-08-2010, 04:12 PM   #17
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Quote:
Originally Posted by dennis
OK. It seems unanimous- engine mount, leading to exhaust noise. Just a few questions: will this cause damage to drivetrain and how difficult is it to replace the mount? Should I replace all? Assuming I should.
I don't think its unanimous.

You should check one more thing, however, before you start spending money.

The muffler has a bracket that mounts to the rear of the transmission.
On my car, the three bolts that support the bracket and muffler are all broken.
When the engine is at the right rpms, these bolts start to rattle, and make one heck of a racket. This rpm point is usually a fast idle speed, so right around 1k rpms.

Take a look.

BC.
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Old 04-08-2010, 04:17 PM   #18
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do you hear the rattle in gear only? Mine is only in gear, which makes me think its due to the engine torquing
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Old 04-21-2010, 07:24 PM   #19
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Mines also rattles in gear on the gas only, 2800 rpm in gears 12&3 everytime o the number?? Gonna beat on the heat shield this weekend.
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Old 04-25-2010, 06:15 AM   #20
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Yep same problem. I ordered a new mount- the 987 mount. I am going to replace it. It has 34k miles and its a 2001 so im thinking due to low use mount rubber dry rotted??

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