MY HERO! Have you changed cables or components or anything that might have affected sensitivity to EMI/RFI? No changes whatsoever. Does it occur with any particular source(s) but not others? Yes. The boiler, fridge, neighbours fridge [adjacent suite] overhead fluorescent light and a fluorescent lamp. The lamp is by far the worst one. An LED lamp has no effect. Neither does an air purifier or humidifier. Have you broken down the system to the most basic unit...just the receiver and speakers connected, nothing else, to see if it still occurs? If OK then, add back one component at a time to try to find the offender. I just swapped out the turntable.The only other component is a Nova II phono stage. I incorrectly assumed that because the noise occurred even when the turntable was off it wasn't the Nova. BUT I WAS WRONGI took your advice and swapped out the RCA's but the issue was still there. I took the Nova out and the problem is gone. I plugged the turntable into both the phono stage and the auxiliary inputs on the amp and turned the lamp on and off several times and then opened the fridge door and let it cycle on and off and NADA. The boiler is fine too. I also noticed a small hum with the Nova in the system when I turn the receiver halfway to full volume that is not there with the onboard phono stage. I'll call Musical Surroundings this morning and see what they have to say. They have very good customer service. Thank you very much whoaru99 With all the other components disconnected, you could even try disconnecting the speaker wires at the receiver and try headphones. About the other receiver, if you exhaust all the above, I would try it regardless of the 4/8 ohm thing. You're not having a crankfest party here, you're just trying to see if you get the same/similar noise problems so there won't be overheating nor abnormally high stress on the receiver just to check this. And, again, I'd start with just the receiver and speakers, nothing else connected. If that works then start adding back components one at a time to try to ID the offender.