Vibration at Certain Speed

[Black_Adder]

This weekend I went on a little road trip with my family, about 1.5 hour drive both ways, and I decided to sit in the back because I didn't really feel like driving (drank a bit too much and slept on a floor the night before). I had felt this vibration/humming/rumble whenever I drove the car to school and went around 100-110Km/h. Well, sitting in the back seat I noticed it a lot more, and it was actually pretty uncomfortable at times.

I'm wondering what might be causing this. I put a new SPT muffler on Friday, and it made the vibration a little less noticeable at the same speeds, but it's definitely there still. Maybe a plugged cat? Rear diff? Anyone else ever have this?

Thanks.

[Airgne]

first check your tires. one could be loose or out of balance. could also have a split tread. i would start there, than look under the car and see if anything is loose. youll be amased at what you find.

[Black_Adder]

I do have one tire that has a shifted belt, located on the rear driver's side. I had the same tire on the front passenger's side, but moved it, and it didn't change the feeling of the vibration at all when moved. I was told about the shifted belt in April when I had the tires balanced. It seems more like something in the drivetrain, because I can feel it through the gas pedal when driving, and not the streering wheel. I'll take a look tomorrow and see if theres anything obvious under the car. I do plan to replace the tire pretty soon as well.

The car, I forgot to mention, is a 1997 GT with a 4EAT.

Thanks.

[Huffer]

Could try replacing the tranny mount...

[1996Battlewagon]

Always do the easiest thing first; replace your tires.

If you still have the problem, then you can start digging. It could be the tranny mount that might have gotten damaged when your exhaust was installed. It could be a worn driveshaft (most likely not though). It could also be worn engine mounts; but you said it only does it at speed and not all the time......right?

It is more than likely your tires though.