2 things could possibly cause this. 1, a dirty speed sensor.
2. If your belt and deck are worn or need lubricant, it can slow down and speed up as you walk. Run the treadmill longer than you walk, without walking on it. If the speed stays constant with no one on it your belt and deck are worn or need lube.
Use napa 8300 silicone
See my video on treadmill maintenance at www.mindbites.com/person/214-Mark
Mark Peterson, March 2008
