I had an irritating little noise coming from my rifle which was probably inaudible to the deer but it kept getting on my wick!! I think it may be the quick release swivels moving about ever so slightly as the studs are smaller than the swivels!!
So tonight I have fitted a couple of O-rings either side of the studs which should stop them moving about. I'm out early tmoro morning before work so will report back, unless it turns out to be something else, like my knees!!