Amsgator,
If there is one thing I found is that the stiffer mounts uncover more problems than most people are willing to put up with. (In some instances, such as mine)
I have a 2002 P5 and THREE of the four mounts were torn to $#it. Originally, I replaced the front and rear mounts (stock to AWR) because I was experiencing some engine shudder and I thought it might be the torn mounts. I changed the F&R mounts and the shudder became way worst. Over a very short period of time the shudder became absolutely unbearable as did the noise that accompanied it. So I changed the passenger-side mount for a stock which I filled. Unfortunately, this only helped make the problem worst.(stooges)
N E way, what I'm getting at is that you should do lots of troubleshooting before making anyone else responsible for what's happened to your car. Check everything. Watch and listen closely to when that noise occurs (IE when accelerating, at a specific RPM, anytime you rev, revving under load, etc)it may be something else loose. If you have a header or after-market exhaust and other torn mounts, this will only transfer the vibration that the mounts took to all other items in that engine bay. Remember, I speak from experience. Since I installed my AWR's, my fan shroud has loosened and its causing an absolute racket.
Remember, it is our decision to purchase after-market equipment for our vehicles and as such, WE take a chance on things not working right.
I'm not trying to knock your character, just trying to ensure that you get to figure out what's happened without getting into spats and blaming sessions. (drinks)
Good luck fixing the problem...