i believe it’s the scopes site that has a long entry on lucille ball picking up transmissions in her teeth. i think cecil has touched on it, too. apparently, it’s a possibility.
As to the OP, maybe you’re hearing the low-pitched Taos Hum (heard elsewhere). . .only you have an up-converter in your head. 
The Taos Hum is supposed to sound like a cement mixer in the distance.
And the sound of breathing in the bedroom? A hidden pervert?
Ray (By the way, how come Mr. Gretchen isn’t married to Mrs. Gretchen, rather than Miss Gretchen?)
You may want to try this link on how shortwave radio can be picked up by various metal objects. It may not be what you experienced, but it’s quite interesting anyway.
http://www.newscientist.com/lastword/answers/lwa1008mysteries.html
In a condo complex where some friends of mine live, there IS a faint beeping sound that comes in periodic intervals. In other words, a short sequence of beeps with a brief pause between each beep. The sequence repeats in periodic intervals.
We all have heard it. It is difficult to track down. (FYI: It is a single-toned “beep”.) I concur that it IS an electronic beep, and we WAG that it is related to the circuitry for power and/or telephone distribution. Although, I cannot imagine what device this would be.