I bought a used 2006 MCS in 2010, it has had a resonant vibration at 2,100 RPM as long as I can remember. It happens in any gear as well as in neutral. It felt like a bad harmonic balancer, so I avoided that engine speed.

Within the last week or so, it started making a "thock" noise when starting out or when upshifting into second gear. It sounded like a bad CV joint or clutch noise.

When checking under the hood last week, I noticed a puddle of oil under the upper engine mount, so I ordered a new (stock) mount from Way Motor Works.

I replaced it today and both the vibration and thock noise is gone!

The car has always had black dried up stuff on the frame rail under the mount, but I thought it might be some black factory goo.

I should have done this 2 years ago.