Vibration issue while driving

[BoostedProf]

I've been dealing with a vibration issue for about a month now. Need help diagnosing where it might be coming from. It happens mostly when I drive between 20mph and 40mph. If I go faster it goes away (but I just think its vibrating faster since I'm moving faster). It does not do it in neutral or at idle. If I drive up to 40 and push the clutch in, it goes away. Doesn't have tire flat spots or bent wheels (wheels are balanced).

So far the car has had its wheels balanced, front lower control arm replaced, driveshaft bolts replaced, and an alignment. Driveshaft bolts were replaced since I saw that they were loose/backing out. I assume (after I looked at the history) that the rear differential was replaced from the previous owner and the bolts were put in but not torqued correctly.

I also saw something about the tone ring TSB recently but after reading it and seeing other people's diagnosing, I don't believe this is the issue.

Best thing I can relate to the vibration is when you drive on a rumble strip on the highway. I have no idea what is could be. Any ideas or has anyone experienced this? NOTE: Car is still under warranty for another year.

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[CorralesR]

I assume no check engine lights? Does it matter what gear you are in while driving 40 mph? Just curious if it's engine speed related. Does it change if you are in 2nd gear going 40 vs 3rd or 4th gear? I'd check the rear hub bearing on both sides. They can rumble like that and they are failry common on the S550s. Although if the vibrations go away at 40 with the clutch pushed in then maybe not the hub bearings.

 

[BoostedProf]

No lights or codes. Doesn't matter what gear im in and it happens after 20mph. It doesnt go away at 40mph, it goes away if I push in the clutch while moving around that speed. Rear wheel bearings are good.

 

[CorralesR]

Hmm. Does it get worse under a load or hard acceleration vs light acceleration? I'm wondering about pinion bearing in the rear differential or maybe output shaft bearing in the transmission.

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