So lately I have noticed some engine vibrations in my car. When I accelerate above 40 is when it really starts. As soon as I let off the gas it stops. I seem to think it may be the harmonic Balancer but I'm not too sure because that's the only time it vibrates. Otherwise you won't notice it at a low speed. Any ideas?

It's a V6 2001

 

If you look at the harmonic balancer while the motor is at idle and when holding at around 2k RPM’s, if you see it wobble even slightly then the balancer is bad and needs to be replaced. Other then the HB, it can also be bad motor and/or tranny mounts. Good luck...