I've got quite a bit of vibration under acceleration. It has gotten progressively worse.
The S is an '05 with 65k greddy kit @ 300whp.
I also noticed my rear wheel sticks out further on the passanger side ( I'd say a 1/4 inch or so)
I noticed it when i put my volks on the car from my old S. It only rubbed on that side. The coilovers are even and the alignment has been checked.
Do these symtopms sound like a bad diff?
What about the rear wheel being shifted?
Any ideas?

Thanks guys!

 

put the rear wheels in the air, check the tires if they have side by side or up and down movement. if it does then its the wheel bearings. usually when those go bad they make a sound though. Is your diff making any weird noises?

Most likely your axles are pitted. get some 2 piece axle spacers and put those in.

 

 

It's not a wheel bearing noise. But I'll check for movement when I have the car in the air tomorrow. The shake/ vibration gets pretty prominent during acceration. The more throttle the more shake. It's smooth when I let off and when I'm just cruising. Just had the car retuned last night. The tuner ruled out it being motor related. It's definately something drivetrain.
I dont hear any noises/whinding from the diff but my exhaust does have a hit of drone. But I'm pretty sure no noises there.
Axles pitted? What does that mean? Common problem? Cause Shaking/vibrations during WOT?

 

Vibration on acceleration is pitted CV joint buckets.

Swap side to side for the fix.

 

Pitted buckets? What occurs when this happens? Do I just swap where the axle goes into the diff from each side?

 

On the right is the axle, with the bucket lifted off. This one is brand new. Yours will be the same, but covered in grease. This is why its best to remove the axles and stand them straight up.

Dont even disturb the grease. Just lift buckets straight up, and switch them. Band clamps can and should be re-used, they are superior design and are made to do so.

on the left is the tool used to pop the lower ball joint, to remove the axle.

TIP: unbolt the abs sensor from the upper A-arm and let it hang. if not, you will break the wiring internally when pulling the knuckle outwards to get the axle out.

 

I have a similar rumble/clucking noise from the rear at 40mph+, under acceleration. Goes away when the clutch is engaged, so something with the drivetrain.
I've replaced my struts with coilovers, replaced rear full axles (with spacers because it's lowered), bearings, upper control arms with adjustable ball joint, and STILL have the problem. Everything has been torqued down (verified with mechanic) and still can't figure it out. Maybe the bearings in the rear differential??
I do have a tear in one of the rear diff bushings, but can't imagine that it would shake the car that much.

Very frustrating spending money with no resolve and seeing my S sit in my driveway in the summertime!!!

 

Where did you get the axles?

If they are not oem Honda, I'll bet that is your problem.

Where are your stock axles?

 

Axles came from www.driveshaftshop.com, which has a long history. Plus the vibration was there with the original OEM axles.