Got a vibration in my 01 v6 vert (17" cobra rims/new tires) here's the details:

speed dependent, not RPM.
starts slightly at 30 MPH and gets progressively worse
shakes seat ALOT (like one of those vibrating chairs at Brookstone), doesn't shake shifter/steering wheel as much
worse on certain roads but regardless of pavement smoothness
seems to get a worse when i shift into 5th gear

WHATS BEEN DONE SO FAR:
brought to mechanic--couldn't find anything-->balanced wheels-->got better for a day or so then got way worse
got tires load balanced and rotated-->better for a week or so-->progressively worse

thinking of first getting tires checked again for a bad tire then going to bring in to a mechanic to check driveshaft balance and u-joints

any other suggestions?? Thanks!

 

Being that it's speed dependent and not RPM dependent makes me think wheels, or possibly suspension... but if you got it balanced and it got better but again got progressively worse, I'm leaning towards something with the wheels, unless your suspension is just being thrown farther and farther out of line. Did you lower the car? Have the alignment done?

 

haven't lowered it. Had it aligned about a year ago, but not since new tires were put on. The car doesn't seem to pull. Mechanic said the suspension looked fine and he suspected the tires/wheels. He balanced them then i had them load balanced later that week. Felt better for a week or so then started getting bad again. ugh. If it makes any sense, i've been hearing a vibration from the rear that sounds like the license plate rattling (have a true dual w/ flowmasters) but the license plate is only fastened with two screws...so that might actually be the reason. Could it be a bad tire?

 

My last truck had a vibration like that. It turned out to be a tire falling apart inside. The tire shop finally found it after the 6th time of going back. The funny thing is they kept telling me it was my truck yet it was perfect before the new tires.

 

Was this dependent on the road surface? For example, would it vibrate on fresh asphalt, but not on concrete? Mine seems to not like certain stretches of highway.

honestly i hope its the tires. The place that did my tires is really cool and i have a warranty until the end of september. Gonna have them come and rebalance and check the tires on tuesday. I figure I'll let the people who will work for free check it out first before taking to a drivetrain mechanic. I also noticed that one tire (passenger rear) was missing a weight.

Only gonna drive it 45 more miles or so to get home. Then I'm not gonna touch it til next week. Don't want to further damage anything.