Do you have the suspension leveling switch that is located to the left of the steering wheel (in USA cars). If you do have it, then you have 2 axle leveling suspension and not single axle leveling suspension (someone correct me on this if I'm wrong). There was an issue with the FTM (technically it's an FTM / RPA - Flat Tire Monitor and not a TPM/RDC - Tire Pressure Monitor) and one axle self leveling cars in the past that I know of, but in your case I would guess it's the ABS sensor. Changing tires has nothing to do with it as it's an indirect pressure monitoring system. The FTM system was implemented from 4/2004 onwards.

reference post #16
http://www.xoutpost.com/bmw-sav-foru...monitor-2.html