Vibration and grinding noise
 

My friends 2001 Boxster S (60,000 miles) was having a very considerable vibration ( the whole car would be vibrating) between 35 an 50 kph and a low frequency type of humming droning noise. The inner CV boot was torn and leaking grease on the right side. I replaced the inner CV joint and both CV boots on the right axle. The vibration is slightly less however the low frequency drone is still there. I had the car on jack stands and had the car in drive and there is a definite humming noise and slight grinding noise seems to be near the transfer case. Could the left side CV joint be causing the noise and vibration? The CV boot on the left side is intact. When driving the car while making a hard right turn the droning noise seems to be less. Would a bad wheel bearing cause vibration? What should be the next step in diagnosis as I don't want to keep changing out parts. The vibration may be related to the front motor mount which I didn't check out yet. However I do think there will still be a problem with one or more of the other CV joints or wheel bearing. Again where should i start with the next step. Thanks.

if you make a hard left turn, is the noise louder? if so, may be the right axle bearing is bad. causing noise and wobble (shaking)

If the front engine mount has never been changed to the new 987 / Cayman mount it needs to be changed. Having the largest concentration of weight moving around in the car causes all sorts of bad things.

Definitely check the front engine mount. If the mount has failed, then the engine can shift around and make very weird grinding noises that sound like a chassis issue.

I have now replaced both inner Cv joints and the engine motor mount. There is a significant improvement from vibration and a grinding noise has been eliminated. However all the problems have not resolved. There is still a droning rumble type of noise and vibration that you can feel through he car. The vibration gets more pronounced as you go faster and the droning is noticeable whether the clutch is in or coasting in neutral and also gets louder as you go faster. A bearing may be the next step however how do you diagnose which one?. Also how do you diagnose whether the outer Cv joints may or not be the problem? Turning right or left doesn't seem to make a significant difference. Is a worn bearing associated with vibration? It appears to be louder from the rear however vibration is also noticed in the steering wheel. Any advice on how to check out the bearings is appreciated. Thanks.

After inspecting the full tire tread surface for anything that can cut your hand, feel the tread surface for irregular wear that has roughed up the tread surface. Non-smooth surface that you can't see but you can feel is bad enough to make roaring noises.

Tires are brand new with less than 500 miles on them.

Wheel bearing(s)?

if my memory is not failing, I recall another thread in this forum that talked about noise due to crushed plate where the inner CV joint attaches to the transmission output flange.
there was a photo with a dimple and the piece should have smooth dish-like feature. I believe it was item 11

Your best friend right here when trying to locate noises..
Digital Diagnostic Stethoscope

Checked out the wheel bearings with a stethoscope and the right rear is failing. Just as soon as the parts get in will change it out. Also had the front wheels needed to be rebalanced, even though the tires were just put on recently and road force balanced. Don't know what happened there. Next steps are to change out the bearing and then get an alignment.

Update. Replaced the right rear bearing and all is good now. It was very surprising how much vibration was being caused by the worn out bearing. Droning noise and vibration are gone. Two things out of this experience I learned is that a stethoscope is invaluable in locating a worn bearing. Droning noise and vibration were associated with the bad bearing. Worst thing about this project was getting the springs back on the emergency brake. There must be a trick to it that I'm not aware about. Car runs great now.