About 1000 miles ago I replaced my rear u-joint. The driveshaft was beginning to vibrate at 60mph and when I took it out, the caps on the rear were cracked in half. I moved the front end of the driveshaft around and it was no big deal, felt fine, so I only replaced the rear universal.

Now, I'm getting some vibration, and even a hum @ low speeds, kinda sounds mean in conjunction with the headers and all. Anyway...

I can hear/feel a small banging here and there underneath. I believe it to be my driveshaft, as sometimes it comes from the front, sometimes it comes from the back (of where the driveshaft would be). However, sometimes it happens when the engine is running and the car is not moving...however if I push the clutch in, it stops.

Even though the car's not moving, would this be the driveshaft? Initially this pulled me away from thinking my driveshaft was screwy, but then I thought about it, and in neutral the tailshaft will turn a bit, but the wheels and vehicle weight prevent the car from moving, but would it be able to move enough (tailshaft) to turn the driveshaft, and with the universal going, cause a banging/tapping noise?

 

Well, if it does it when the car isn't moving, I'd say you can rule out the drive shaft and the U-Joints, which leaves transmission and the clutch and if it stops when the clutch is engaged its probably in the throwout bearing and flywheel area.

Actually, I don't know what I'm talking about, but you need to go through the process of elimination in order to narrow it down.

For example, we probably can rule out the headlights.

 

At first I thought it might have been related to the transmission input shaft/clutch, but the tapping noise happens toward the rear of the car (under the center console or in the hump in the back seat, but before the rear end). I'm fairly certain it's gotta be the universal on the front end, either that or the driveshaft became pretty damn unbalanced.

 

If it does it while your not moving then I suggest you replace your tranny mount. The vibration from your motor is probably shaking the end of the tranny and it hitting your car from underneath. I should know, it happened to me

 

I would think it's not the tranny mount as that's less than 1 year old, but I'll give it a look.