so occasionally, not all the time.. but every so often i'll get a really bad vibration that sounds like it's coming from the back end of the car.. it'll idle around 1000RPM and it won't go away unless i step on the gas. sounds like it's coming from the exhaust if i had to say.. any ideas what this could be?

 

Do you have an aftermarket exhaust system?

 

mm.. i have the ninosport dual exhaust conversion with GT takeoffs.. that's all

 

Same thing happens to me. I have older Flowmaster 40's.

But, nothing seems wrong, just an annoyance.

 

same here i just firgured it was resonance drone but its pretty bad to be that. I have a single flowmaster american thunder muffler

 

Check all the exhaust hanger bolts (if you haven't already)

Also check that the exhaust expanding when it's hot (it'll actually stretch a bit as it warms up) isn't causing the hanger rods to touch either the metal part of the hanger, or the sheetmetal behind the rear bumper. Had all of the above at various times with aftermarket exhaust on my car.