220 MHR???

I think you have a false reading too but I would suggest that it is weaker signal to the heart monitor rather than higher external noise that caused it.

I have an HRM that stores all the heart rate data for down loading to a computer.    When I get a really high number, it is usually an isolated spike occurring really early in the run.  I reason that the problem here is poor electrical contact with my chest because I haven't started sweating a lot yet.  Poor contact means that the heart true heart signal is weak.  The monitor always has to select the true signal from noise.  When the true signal and noise are in the same range, the monitor sometimes picks up a noise spike as a heart signal resulting in a high HRM number.

TW

I often get funny readings when the electrodes aren't making contact  just right. Always when running...usually a few tugs get rid of the problem (looks pretty bad when I am pulling at my bra, but hey, can't help it)  Worst reading came out at 288!!!!!!!!

Jen

TechGeezer's got it right...beginning of the run before the signal becomes 'stable' due to intermittent contact.  Also, I've had this toward the end of the run when the HRM slips down a bit - but once you reposition and it makes contact again it usually goes away (one time it didn't, at the end of a marathon, coincidentally, and it was because I dried out due to a great headwind as we were coming in - all the fluid evaporated, and again, no electrical contact).  One really fast way to check is next time you see that reading, stop for 10 seconds (a small price to pay, huh, for potentially carnal knowledge about how you work) and manually count the beats...

I did, however, have a friend (who has since moved away) who, at age 32, had a max HR of 228.  Saw it with my own eyes, tried him on 2 different monitors.  Guess he was just set up that way....but you could see his HR rise up to that level...it wasn't at 145 then all of a sudden end up at 220+...