This was new info to me shortly after buying our 530xi E61 a few months ago. Scared the piss out of me, but so glad it prompted me to inspect things. Belt was getting chewed up on the inside. Turned out a shop or PO had installed a junkyard AC compressor that must have come from a car that had been hit pretty good in the front. The pulley was not true. I don't know how long that belt would have lasted (I had already ordered a replacement, along with plugs, coils, VC gasket, etc, etc) but knowing about the ingestion problem made me glad I had checked it out. New AC compressor pulley and it's back good to go now. But... things could have gone south in a hurry.

__________________
2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)