Could be low on power steering fluid, check that first. If you need to add some, make absolutely certain you have the correct fluid. Some BMWs use automatic transmission fluid instead of power steering fluid...and there are myriads of types of ATF and PS fluids...you need to use the correct type. Get out the owners manual and read up on how to check the fluid and what type it requires.
540 M-Sport package (Canadian market), factory Bluetooth phone kit, factory M-Audio 10" dual voice coil subs, Homelink, M5 rear stabilizer bar, H&R 15mm spacers, Bilstein B14 PSS coil overs, Stop Tech ss brake lines, Akebono Euro Ceramic brake pads, oem Brembo and Zimmerman rotors, Dinan Stage 1 software, Strong Strut front upper stress bar, USA Spec Ipod/Iphone integration.