On Mar 20, 6:43*pm, TomC wrote:
"Martin C." wrote :


I use to have a similar problem and it turned out to be a possessed
woodpecker. For some strange reason the darned bird liked the sound. He
would peck on the metal chimmney cap. Could count on him to stop by several
times during the season and let us know that he was still around.
TomC

This is exactly what came to my mind when I started reading the OP.
If there is any critter that can simulate a machine gun (or I guess a
low gutteral BURP) it is a woodpecker.

RonB