Maybe that's what it is...but i can hear it clear as day through several walls in a quiet house. I know the buzz in the flourescents you're talking about and those are very easy for me, almost sounds like a fly next to your ear, but these frquencies im talking about seem to be much, much higher that, no?
The perception of super audible frequencies is mostly through bone conduction I believe. Odds are what you are hearing is below 20kHz. Humans are unable to detect the pitch of sound above 5kHz, so that will give you an idea of how high up in the spectrum we're talking about.