I just started driving my '91 N/A a few days ago after spending the last 4 months building the engine, etc., and I've been noticing a very annoying/ disturbing rumbling noise that I can feel in the car ONLY DURING DECELERATION. As soon as I start giving it gas everytime I feel it, it goes away. If I remember correctly, I start feeling it and hearing it over 30 or 40 MPH or so and faster. I really tend to notice it on the highway when I'm cruising along at a good speed (60-80 mph). I originally suspected bad u-joints, but it only happens when I let off the gas. I'm guessing bad differential or bad driveshaft.
Any ideas??

Brian

 

Bad front diff mount, compounding with a U-joint problem. Or at least that's my semi educated guess. These types of issues could be ANYTHING suspension related, so you need to check every bearing, bushing, etc. Could also be clutch release/pilot bearing, or any number of shafts/bearings in the transmission.

 

Strange thing is that I haven't been noticing it all that much lately.....nowhere near as much as I did when I first started driving the car.