The antenna's too close.
I have an SWL antenna outside my bedroom that just happens to resonate on 20 and would make a pretty darn good antenna if it was more than 12' off the ground. I didn't put it up for DX'ing, it's just a quick & dirty 66' of #18 wire fed a quarter wave from the end nearest the house.
It loads well enough that I can hear myself in the bedroom stereo through a large pair of three way speakers if I run more than ~50 watts. Did I mention the stereo does not need to be turned on? Tis' true. The speaker wires alone pick up enough RF to give me plenty of volume through both speakers with the left side being the loudest. That's what I call RF coupling, and yes, the left speaker is closest to the antenna. Like maybe 4' - 5' if I had an X-Ray tape measure. The antenna does have a 1:1 balun at the feed point and is a clean install by an experienced amateur with above average intelligence and exceptional good looks.
It's just too damned close to the speakers, and the answers I'm sure you'll get about ferrites on the power cords and such address the symptoms............. Not the cause.
Either crank the power down or get the antenna away from the house where it belongs. It's an outdoor toy.