In the meantime, I removed the serpentine belt - it is in great condition. The bearings in the tensioner are a little worn - but not terribly so. Both left and right deflection pulleys are in OK condition - maybe a little less worn than the tensioner pulleys. I cannot detect any issues with the alternator, PS pump, AC compressor.
My plan is to replace the 4 'routine maintenance' parts (belt, tensioner, both deflection pulleys) and see if the issue is resolved.
FYI, there is no evidence of the powersteering pump pulley having collided with the sub frame.
2007 E90 335xi
Cobb AccessPort, BMW Performance Exhaust