Check this sticky thread for all known issues related to 1M or better, keep a print out with you while checking the car:
http://www.1addicts.com/forums/showthread.php?t=760815
I had no issues with mine so far, not even a rattle, in general it is one of the most solid built BMWs with occasional issues reported.
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"The mark of a great car is one whose overall competence exceeds what you should expect from its individual components and the 1M does just that", Chris Harris.
BMW 1M-SOLD-: TECH: Evolve Race+N55mids, Evolve IC, Michelin PSS, ER cp, aFe filter, CDVx, Vorshlag camber plates, BMS OCC EXTERIOR: trunk spoiler, blacklines, black grills, IND goodies INTERIOR: Alcantara steering wheel, steel pedals, custom mats, MPower e-brake.