I have a strange noise coming from my wall behind a kitchen cupboard. It sounds like there is a small jackhammer inside the wall that goes on any time of day and night. It is a very fast low pitched jackhammer like noise that has been going on for months. It stops sometimes for a couple of days but then starts up again. It was quiet for the winter but back in March. We see no signs of bees or ants outside or in the basement where the noise persists. Any suggestions?

It sounds like you may have some air in your plumbing inside of that wall. The only thing that I can imagine making a noise like the one you've described is a woodpecker!?