Rearend feels loose and uncontroled.
I had this same problem with my E46 M3 and it turned out to be a severly bent rear lower control arm. It was bent when the tow driver tied down the car using the lower control arm. I checked everything and nothing looks bent or loose.
When I am in any gear and I go WOT the front seems to pull to the right. Normally, at WOT the rear will sit down and the front come up evenly and that is not the case with my car right now.
The rear end also feels unstable. It doesn't feel loose but unstable is about the only way I can explain it.
I have the following suspension mods:
BMW Performance Suspension - about 6 months old
ARC-8's with Michelin Pilot Super Sports
Front alignment pin delete for negative camber