I have been using the chest strap monitor with my TomTom Spark/Runner 2 since mid January. For the first 6 weeks it worked fine. Then it started to give faulty heart rate readings. It spikes real high and drops real low during a run. Usually after a mile or so it straightens out, but not always. I changed the batteries and I still have issues. I have wet the strap contacts and that does not help. It occurs whether I am indoors on the treadmill or outside running on a trail, so I don't think it has anything to do with interference. Anyone else dealing with this? Any suggestions on how to fix this?