I get this periodically on mine as well. I beleive - at least on my - it occurs when the ball is loaded into the gun, but manages to dribble out the barrel onto the pf. The rotation of the gun seems to stop at varying locations each time and sometimes it points more toward the left allowing the ball to drop out. My guess is that this causes some sort of fault condition to be recorded as I will usually see this error sometime after it happens. Typically a few more games where the gun gets loaded correctly will cause the fault to go away by itself.

As for the noise you are hearing, I don't encounter this. It may be something you want to look at. I would first look at the turret parts to make sure they aren't worn, broken, or put together incorrectly.

wow...that was a good find. Way to troubleshoot. I find accomplishments like this under the pf almost as rewarding as those on top of it.