I'm going to tell you a story...... if it is useful.... great. If not.... sorry.
Several months ago I decided to set up one of my TRC-458's that I got last year. I wanted to put it on the desk with my ham radios.
So, since the TRC-458 had the biggest footprint... I set it straight on the desk and set my Icom IC-7300 right on top of it. Messed around with the 458 for a while.
Some days later... I went in and turned on the Icom.... got on 20 meters.... and keyed up to send a CQ call. The instant I keyed up.... the clothes washer.... two rooms away..... broke out into a loud buzz. It was the off balance buzzer.....stuck on full. When I walked in... the red "LOCK" light was lit...and the machine completely failed to respond to anything on the control panel. I reached down and unplugged it, let it reset, then plugged it in again.... silence...and the machine was ready to go.
I went back to the radio.... resumed trying CQ calls. The instant I keyed up... the clothes washer lit off again. Same thing.... off balance buzzer stuck on.... "LOCK" light lit. I reset it AGAIN.
I sat down in front of the radios...and assessed the situation. I had used the Icom MANY times with no problem. THIS however.... was the FIRST time I tried it since setting it on top of the TRC-458.
I removed the TRC-458 (removed the coax, unplugged it from the wall, removed it from the desk and put it on a shelf across the room). I then keyed up the Icom.... nothing. Silence. I mean.... the ICOM worked......but no "chiming in" from the clothes washer.
The only "wild guess" that I could come up with was....... when I keyed the Icom.... RF was coupling from the Icom to the 458...and SOMEHOW getting back into the AC wall plug and on into the house wiring....back to the breaker box (the two items were on separate circuits!)....and apparently the washer was sensing it and behaving badly. But as soon as I removed the 458 from the desk ... that was the end of it. I can now work on the Icom...full power ... with no problem...and no objections from the clothes washer.
[edited to add] and by the way... the TRC-458 was powered OFF during this exercise. It was NOT on.