I'm not sure this is the right forum to ask, but I decided to start here and repost elsewhere if necessary.
After decades as a Technician, I finally did the paperwork to "instant-upgrade" to General (I got my license back when the Tech exam was the General written and Novice CW). I've never had an HF rig until a week ago, when I bought an IC-7100 because interfacing as as simple as plugging in a USB cable and it also covered VHF/UHF bands.
My wife wasn't happy with my original idea of a long wire antenna hanging above our pool, so I put an 40/20/10 dipole in the attic (a G5RV junior). It's slightly inverted, as the 51 ft length was just a bit longer than our attic, corner to corner. It's working well enough for PSK31 on 40m and 20m, at only 20W. PSKReporter monitors reported hearing my signal across the continental US. And, I just made an FT8 contact on 20m with only 5W. I looked at PSKReporter, and I was stunned at the number of stations that heard it.
But, there's an interesting side effect: when transmitting, the fan on our AC/heater starts running. The AC/heater is in our attic (normal around here), and the dipole doesn't quite straddle it, but it's 3-5 feet away (horizontally). Another AC/heater (for the other part of the house) doesn't run, but it's about 10 feet farther away. I haven't yet determined if the AC compressor unit (outside) turns on, as I'm limited in what I can see/hear from the control point.
I'm not sure where to start. I suspect it is the control line from our Nest thermostat. But, I was hoping that someone else dealing with antenna restrictions had encountered a similar problem. Any suggestions?