Question
Beginning in May, 2006, we noticed a pretty loud drilling-like noise in my son's bedroom (2nd floor 1915 "farm house" in Arlington, VA).  There seems to be no rhymm or reason to when we hear it now -- in the beginning it seemed to be only in daytime, and sometimes we don't hear or notice it for a few days and think it is gone.  The sound is concentrated midway between floor and ceiling (it's so loud you can hear it in other parts of the house).  The closest thing I can compare it to is the sound of a masonry bit in concrete when you're in a building and the work is several floors away.  It will last a second to a few seconds, repeat (randomly) a few times, stop for a while, come back.  As far as I know there is nothing mechanical in this wall; you can't hear the sound at all in the attic.  We thought perhaps woodpeckers, carpenter bees, borers; pest inspectors could not figure it out.  One said must be mechanical.  I'm at a loss.  Any suggestions are appreciated.  Besides being annoying, I'm afraid damage may be being done to the house.  Help!

Answer
Well I would not rule out the mechanical cause just yet. My question is who did you hire when you hired a pest inspector.  If you hired a bug man then chances are he/she didn't climb the roof or put a ladder up to see if there was any openning in the house. Few inspections are complete without a ladder being thrown up. If animals are ruled out then the next question would be insects or mechanical. I doubt the inspection was of the standard I am speaking of. visit http://icwdm.org click on solutions and you will see links to how to inspect a building and how to hire a professional.

Ultimately, you may need to get a fiberoptic scope to take a look in the wall.