Jim wrote:


In my case, we have cable TV and I've only noticed the noise on AM radio. The
noise is quite on all stations except for a 50,000 W station 2 miles away, and
even on that station the furnace noise is audible in the background.

Correction: noise is quite *loud* on all stations.

I should add that the American Standard AUY (also known as the Trane XV90) furnace
series is a natural gas furnace with a variable DC brushless blower fan motor. The
inducer motor is variable too, but it may be a brush type motor, causing the
noise. It must be quite a bit because it causes interference on the radio in my
car as I approach the house.