ok - this is the twlight zone people. i just purchased this house, built in 1955. i hear the faint hum sound in middle of night, early morning. turns on for few minutes then off. will be off for several hours and return. don't hear it during day and its in my bdrm, back of house. thought maybe a sump pump but don't see any evidence of that. or what the blip? i have no idea. electric bill is pretty norm for usage. i'm with you wtf - i have no clue. have to get brave and crawl under house for peace of mind i guess.