I have the Polar HRM, which I have been using for several months now. I recently, however, started doing high intensity interval training on the treadmill, which involves getting my heart rate up to 90% of the maximum. When I do, and it gets above 161 or so, I get a "check transmitter" message. It then starts working again when I alternate to slow and my rate comes back down. Anyone else had this issue? I can't find anything in the manual or on the website talking about this issue. I am frustrated because the higher end of my range is where I need the readout the most. Any help appreciated. Thanks!