I just got a new Garmin 500 and noticed that after I finish a ride (when I'm watching it) and park my bike in the foyer it shows a speed of 0 mph for a few seconds, but begins to randomly gain speed (5-10 mph). Also the grade function on my Garmin is being strange (I think it might be calibration), but gives readings of 700+% for short periods of time, especially at the beginning of a ride.
Any ideas as to what the problem is?