OK long story short, this past weekend we just had a huge snow. Finally my first opportunity to see what the S has got. She did AWESOME! That was until monday morning on my way to work. Every bump I hit due to the icy bumpy roads of Southern NJ is like a stab in the side as I understand what the sound I am hearing should be... oh crap it sounds like I have something undone in my rear suspension. Every bump brings on a loud and hard thump heard throughout the inside of the car.

I get her home nice and easy. After putting the suspicious passenger rear of the car in the air and taking off the tire, i find everything to be in perfect health. Every bolt seems tight, every joint looking pretty.. nothing to lead me to think i ripped something off the body, lost a bolt, blew a shock, etc. I crawled under the car, the diff seems fine, the tire is fine, the shock isnt leaking, no spring damage, nothing is wrong! I put the tire back on, go for a drive and I still hear the thump. I took everything out of my trunk and made sure the spare is down tight.

At this point I am swamped with work and just need the issue taken care of, so my dad takes her to my local shop while I am at work. He knows the noise that I am talking about and explains it just as I did to the mechanic when I made the appointment. I come home to my car in the driveway. The mech says he didnt hear a thing during the drive, so he threw her on the lift and he said everything in my rear suspension is fine. so I take her out for another spin to confirm my reservation at the nut house and lo and behold, the thump is still there.

so now what? My local mech says everything seems fine, i see nothing wrong, but there definately is a thud when hitting bumps. Now I am the third owner of the car so I am not 100% on the suspension setup, but this is what i do know. she is lowered and has Bilstein SP's (atleast 6 yrs old) on her with what I am assuming is lowering springs because I am not sure just the Bilsteins would lower the car. I also did have an alignment done a week prior to the snow storm.

I did hear the thump all weekend during the snow storm, even before I started having fun, but i just assumed it was from the unplowed roads and was normal until i got on the smooth plowed roads monday morning.

I have gone through just about every thread I could find describing weird noises from the rear and looked everywhere and tried everything with no satisfaction. The rear does not bounce weird to suggest a blown shock. Also something weird I noticed, perhaps because I am a little paranoid now and looking for things wrong, perhaps not, but when I get on her it almost feels as though the *** sags...?

Anyone have any other suggestions cuz I am fresh out.

 

Here's an idea but it will take more wrenching that you were hoping for - remove and disassemble the rear shocks, maybe a defect emerges that you can't really see when the whole system is under load.

You could also swap the coil/strut to the other side and see if the problem moves to that side. If not you'd at least eliminate one variable from the list.

 

Perhaps over the long weekend, I will give it a try.

 

I wish I had a better suggestion for you. The thing is, the rear suspension is really not that complicated compared to the front. If all of the bolts are tight and none of the joints are clearly worn out then there's not much else to look for.

It is possible that your coil is actually is cracked somewhere - if it is just a partial crack then the spring would still appear to be fine but as soon as load is applied to it it would essentially fail to do its job. This could cause the sagging you think you're seeing and the thump may simply be the tire hitting the inside of the wheel well because the spring no longer applies any counter force over bumps.

That's my theory anyway, not totally unheard of in 6 year old springs, but it would be rare.

 

Just a stab in the dark, i recently had rear suspension issues after havin a new set of KW coilovers fitted, it turned out the lower bush on the shock was ever so slightly oversized it sounded just like a loose bolt and it went back to the garage a number of times, finally dismantled the whole rear assembly to discover a wear mark on the bottom bolt/bush. Turns out needed to replace both rear shocks under warranty. You say its not a new set up but thought i would share that to try and shed some light...