The Underlying Tone

So I was pulled from sleep at 4am by the regular symphony of birds outside our bedroom window.  Normally I would have been able to fall back asleep with ease but there was something different in the air.  My left ear was picking up a set of electronic beeps that were extremely faint but very patterned.  My guess of why only my left ear could hear it is that my right ear has been damaged slightly more through my years in the service with heavy and light weaponry.  Since it was also only heard the the left ear it made it very difficult to pinpoint the origin of the beeps.  So I fought back by rolling over and putting my left ear to the pillow.  This movement was just enough to block the extremely faint sound of whatever and wherever it was.  In moments I was back to sleep.  Now that I am awake again I can not seem to find the sound.  Maybe there is much more going on during the day that interrupts the wave from reaching my apartment.  This means that whatever the sound was its origins were outside my apartment entering through the glass of my bedroom window.