My 99 STS has always had a minor oscillation over bumps.
Specifically, broken pavement leads to a shimmy felt throughout the
car. Kind of feels like marbles rolling around underneath you.

When this happened to my 71 Cutlass, it was front wheel bearings.
My struts seem fine ... no floating. Obviously some suspension
component has failed at 107k. The car drives flawlessly on the highway.
Problem only comes up around town on our frost heaved pavement.

Any thoughts as to where I should look?

Thanks in advance.

Go to the suspension forum, and check out the shake shimmy STS thread. See if the symptoms match up.

Don

Go to the suspension forum, and check out the shake shimmy STS thread. See if the symptoms match up.

Don

I read and participated in the main thread, which really concentrates on the 65-70-mph vibration.
My issue is different ... however, I'll try posting in the suspension forum.

Rear bushings did it on my Eldorado.