Did a quick test of AM radio in my car over the weekend. My radio reaches 1710khz, and there is a bit of high pitch noise when I get close to my driveway spot at my basement. There's also a looped 'bloop' noise that repeats almost every second.
I'll try unplugging the Western Digital network switch I have that hooks up the family room equipment and see if that makes a difference. Can't think of much else that's ungrounded..
Making a dipole tonight time permitting.