No experience on solid mounts on a street car. The competition cars I've had them in, it does seem more like constant hum or drone along with a more solid "whack" instead of a thump when going of bumps and such. But we also had bronze bushings through out and not just in a single place, so every movement was amplified

Personal sensitivity to it will also be a factor. My hearing is shot, so there is a lot of noise I miss that others may not. I've even seen guys here on moparts complain that hemi sized torsion bars were too stiff, so we all have a personal baseline to work with.