Was the noise just when switching between cooling and heating in the test mode, or does it do it in normal operation?
It seems to only make the noise when it is switching from cool to heat. It had previously been running in heat mode and when I had the thermostat call for heat this morning it did not make the noise.
I waited awhile and then switched to cool mode through the tstat and ran the AC for several minutes. When I switched back and had the tstat call for heat the noise was there again for a minute or so. Went back half an hour later and called for heat again and it was barely audible, and only for a second or two.