I did a search but everyones problem seems different. I have a 2000 civic si when i get to 70 mhp i get a weird vibration. The thing is if i get it up to 80 or more it stops. I just had an alignment done and rotors put on a couple weeks ago. Any help would be appreciated.

 

speed dependent vibrations are typically balance related.

the only other thing to look for is some blister or out of round on the tires.