Have a Car Question? Ask a Mechanic Online.
ign = ignition
As I stated in the last post check for a bad U joint in the drive shaft (could be drive train related u joints do cause vibrations at cetain speeds and speed of vibration can change)
Start it up, step on the brake, shift From Reverse to Drive a few times and listen for distinct clunk noise if so it would be your driveshaft U-Joint, you can also raise your vehicle secure it with jackstands and try turning driveshaft by hand and look for play at U-Joints also look for rust around U-Joint caps.
If you can see or hear any of these symtoms you have to replace the U-Joints.
If none of these symptoms are there then I would check your tires for missing balance weights when your tires are out of balance it will also make your vehicle vibrate at certain speeds.