Powerflex rear upper shock mounts:
https://www.bavauto.com/bmw-shock-mount-pfr541612
Strongflex front thrust arm bushings:
https://www.strongflex.eu/en/e90-e91...553503470.html
The shock mounts were installed by myself but I had a shop install the thrust arm bushings because you need a big-ass press to push the bushings into place. As I mentioned, I do have minor creaking from the Strongflex after being parked but it's minor and bearable. If you want something OEM-like quiet you have to pay over $500 for real bearings:
https://syncrodesignworks.com/collec...ro-thrust-arms. I'd love to do the Synro arms, but the cost is a big deterrent since I could R&R Strongflex bushings half a dozen times for that cost !
Doing these poly mods made noticeable improvements, but it was only after I installed M3 rear end parts (rear subframe bushings, antisway bar, upper control arms) that made the car feel rock solid under hard driving. But this last mod is the most expensive at somewhere around $2k. The poly bushings are a bargain in comparison