mm wrote:
I have a standard POTS line for a phone and if the extensions in the
basement and main bedroom are plugged in, the phones in the kitchen
and office play WBAL AM radio, 1090.

Easiest is to find a DSL line filter. They're just the right specs for
killing AM band signals. Plug it in series with the loudest phone.

If you can't get one of those, try a 0.01uF to 0.05uF capacitor,
across the red and green wires. You may need one at EACH phone jack.

Way back when I used to live in the shadow of a 50KW AM station, it
took a pair of capacitors across the phone line, with 2.5mH chokes in
series, to eliminate the background chatter. But you can probably get
by with less than that.