For a couple months now, whenever I put a decent amount of load on the back end when accelerating (launching for harder acceleration and even just starting uphill from a stop) there is something hitting pretty hard under the rear of my car. I had an SLP Loudmouth system put on last summer but this just started a couple months ago. Took it to a Chevy dealer (it was my LAST resort, long story) upon which the mechanic said that it was all just really hard backfires coming through my exhaust that i was feeling I have a VERY hard time believing that though. However, I have no idea what the hell it could be. Nothing hits when I shake my exhaust system. A couple people have suggested it could be tranny mounts, but what ELSE could it possibly be so that I can take it somewhere else soon and have them check a full list of possibilities? Thanks guys.

 

I had a tranny mount issue exhibit similar characteristics. Also, check the rear end. A missing tooth or two will do this...right before it leaves you stranded.

 

Hey, i had a similar problem, little while ago, and it ended up being the torque arm bolts werent tightened down, to the rearend all the way. They were just there and i tightened them up and solved the problem. Hope that helps

 

+2 for tranny mount...my car I thought it was the rear end. Replaced the torque arms with BMR. Poly torque arm bushings...turned to be the stupid tranny mount...replaced with a 1LE mount from GM.

1998 GSM Z28