Dodgy M3 Speedo ??

[chuckh]

Ive recentley bought an E46 M3 convertible 2003 44 k miles, On a couple of occasions the speedo does not drop to zero when stationary ! It may drop to 30 mph the drasticaly overeads when I resume driving Then when parked up it will ovenight return to zero and work normaly !!!! Anyone had this happen or any thoughts ??? Thanks