2000 Jeep Cherokee AM radio noise

2000 Jeep Cherokee

I have am radio noise. Almost sounds like distributor noise I used to get in one of my old cars. A high pitched mosquito noise or whining. Except it doesn't change with engine speed. It comes and goes. Strangely sometimes it will go away when I step on the gas pedal. If I take my foot off, it comes back, then goes away if I use pedal again. And at other times, it just stays constant. Gas pedal has no effect. Do you know cause and cure. Thanks.