Car vibrating at 60-70 mph

[lorszulak]

I know there are ton of threads on this but I think my case is different. History, its a 2004 pontiac vibe gt with ACT clutch and Fidanza flywheel with eibach lowering springs. All those mods were done around 100k miles, car now has 215k.Symptom. Just started to happen out of the blue, car shakes at 60-70 mph. If I accelerate harder it vibrates more, If I push in the clutch the vibration stops. So it only happens under load, not sure what that means. Could it be the tire balance, CV axles, etc. Let me know what you guys think. I find it weird that If i disengage the clutch the vibration stops leading me to believe it is the CV axles... But when I turn the steering wheel there is no clicking sound which usually would indicate a bad CV axle. Also I can drive on the street doing 50mph fine no vibration its just at that magic 60-70 MPH. Now today it is starting to make a thump thump thump thump sound like if its getting worse.Any help much appreciated.

[star_deceiver]

Check your tires!!! Bulges, tread seperation, flat spots, balance! Also check the motor/transmission mounts and INNER cv joints

[sideshowalan]

Rule the tires out. Those would shake the car whether the clutch is in or out.Sounds like axle to me too but it's strange that they're not clicking. I would recommend further inspection of the axles.Check all 4 boots for tears or grease. Or find an empty parking lot, roll the windows down and listen for the click while driving in tight slow circles both forwards and backwards.

[lorszulak]

sideshowalan- thats what I thought about the tires too. If it doesnt vibrate when I disengage the clutch it cant be the tires, well I have to wait until the weekend to pull the axles out. Ill let you guys know what happens.