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Old 08-03-2016, 05:16 AM   #1
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Buzzing sound when hot and under acceleration

I have a 2002 Boxster S that once the car warms up I start get this buzzing sound when under acceleration. I can tolerate it until I pass by a fence or any kind of reflective surface and the sound bounces back to me. It really diminishes my experience of the car and I find it embarrassing. I had it looked at and nothing obvious has been found. I suspect it's originating from the exhaust system, but had that checked out and nothing of note found there either. Anyone have a similar issue that they were able to correct?
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Old 08-03-2016, 06:25 AM   #2
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Exhaust would be my guess as well, but I have heard that a loose spark plug can generate a buzzing type sound as well.
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Old 08-03-2016, 06:37 AM   #3
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Anything that shifts in size with higher temp and creates a self resonance at a certain vibration speed.

Does it reoccur if you stand still in neutral and increase throttle slowly throughout the register? Does it make different sounds depending on the surface quality, rougher tarmac etc?

It could be a heat shield, something inside exhaust system for sure.
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Old 08-03-2016, 07:07 AM   #4
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Thanks guys, looks like I have some homework to do. I'll have to take it out soon & try some of the proposed troubleshooting.

Getting a little ahead of myself but got all excited when I viewed this video on YouTube where a British outfit found a kit that replaces the entire exhaust for 600 pounds (not quite $1000 U.S.). But damned if I can figure out where they got it. https://www.youtube.com/watch?v=oS_yKQRcln0 30:33 mark. Probably wouldn't meet U.S. spec anyway but was hopeful I could find something equivalent in U.S.
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Old 08-03-2016, 07:16 AM   #5
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Exhaust would be my guess as well, but I have heard that a loose spark plug can generate a buzzing type sound as well.
Looked into 3rd party exhaust packages but they're all uber expensive
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Old 08-03-2016, 07:17 AM   #6
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Anything that shifts in size with higher temp and creates a self resonance at a certain vibration speed.

Does it reoccur if you stand still in neutral and increase throttle slowly throughout the register? Does it make different sounds depending on the surface quality, rougher tarmac etc?

It could be a heat shield, something inside exhaust system for sure.
I'll take it out this weekend to do a more thorough analysis, thanks!
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Old 08-03-2016, 11:06 AM   #7
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+1 on the heat shield
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Old 08-03-2016, 12:26 PM   #8
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+1 Heat shield or/+ exhaust. That's an easy and cheap fix hopefully.
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Old 08-03-2016, 12:43 PM   #9
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+1 on the heat shield
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+1 Heat shield or/+ exhaust. That's an easy and cheap fix hopefully.
You guys are great!

You know, I'm good with the electrical things; replaced a failed ignition switch & seat belt receptacles due to an error code but mechanical is a whole other issue, lol.

How would I trouble shoot a heat shield? I take it you're referring to the ones on the back sides of the cats? Could I maybe get some large SS hole clamps and tighten them around the cats to prevent potential rattles? How would I troubleshoot the exhaust?
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Old 08-03-2016, 01:39 PM   #10
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Rubber mallet and hit it gently all around exhaust and listen for vibrations
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Old 08-03-2016, 01:47 PM   #11
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Rubber mallet and hit it gently all around exhaust and listen for vibrations
Thank you. Yes, first thing my mechanic did and everything checked out. Key seems to be it only happens once the engine/exhaust gets hot.
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Old 08-03-2016, 07:41 PM   #12
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I have a similar or same thing happening in my 2001 2.7 5-speed, and since I haven't fixed it yet I can't be quite confident really at all what it is, I can say I've ruled out a bunch of things I've already tried and looked closely at.

First off, the noise only happens when engine is warmed up (or even better yet, HOT), is much more pronounced the more the throttle, (needs to be really hot to do it free-revving, without any loading), and also only in a certain rpm range (and in multiple, dint inch resonance bands within that range). Seems to be in the 2000-3000 rpm area, maybe three peak resonance bands in there about 200 rpm or so apart. Sound is a metallic rattle, sounds just like a rattling heat shield, most noticeable when driving by something reflective and with the top down. Seems to be coming from the passenger side. At first I thought it coming from back, but further diagnosis, indicates it coming seemingly from up by the motor, much higher up, perhaps up near the exhaust manifold or even above it somehow.

It's been driving me crazy, although not bad enough to stop everything else to fix it, and I've already looked at heat shields (quite a few of them). If not something with the exhaust manifold, I've wondered if could be accessory drive belt (like power steering pump or water pump), or even dual-mass flywheel pieces. I've pretty much ruled out exhaust, though. Problem is when I get it up on jackstands to diagnose it, by then the engine has cooled off enough all I can get is a faint sound if I can get it to reproduce at all. Same goes for removing the top or front engine cover. Sorry I don't have the answers, but at least know you're not alone.
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Last edited by jakeru; 08-03-2016 at 07:43 PM.
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Old 08-03-2016, 08:02 PM   #13
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I had a buzzing rattling noise from my car that I simply could not find. Decided to upgrade to a 986S muffler and whoa and behold found I had something rolling inside the original exhaust. Sounds like a rock but I have not taken the time to see what it is. I figured someone tossed it in there for the PO.
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