Well at about 80 and above it seems like it vibrates just a little bit. im not sure what its from but I can hear stuff in the rear rattle and my console rattle a lil bit. Its not a huge vibration but its one of those things thats annoying. Im not sure if its gets better at higher speeds but it didnt seem to change when i got up to 100. The car is a 96 and it has 77000 miles on it

 

3 possibilities...

1. Get your wheels properly balanced.

2. Bad tranny mount or if your using the ES mount you should expect some.

3. You've got a very imbalanced driveshaft so it's time to upgrade to a LS1 DS or the 1LE.

 

I have the same problem...it can also be the U-Joints going bad

 

It does sound like my U joints are starting to go, but i do plan on a poly mount and a ls1 driveshaft.