I recently replaced the all four subframe mounts, all three diff. bushings, shocks, rear diff. fluid and sway bar links. Car handles great now. However, It sounds like I am being chased by a freight train. It sounds like harmonic noise. It is so loud it drowns out the radio. It is not as loud when I let off the accelerator and it starts to go away above 80 MPH. The only thing I see from the shop manual pics. that I did not do right was the shim on the front diff mount. It is supposed to be between the diff and the bottom of the two piece bushing. I have it on top of the subframe under the top bushing.
I am going to move it tonight.
Could this one piece being out of place be transmitting all this noise through the subframe and body?

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1987 300D 146K Original #14 Head
One eye on the road, the other on the temp. gauge

Gone But Not Forgotten
1983 380 SEL Long gone
1983 300SD Wish I hadn't traded it in on a 90' Corvette
1989 300SE My all time favorite
1995 E420 Went like a bullet