Yal - The idle valve and OVP has been changed. I too think its running rich and plan to screw the CO down (not literally though). Will do that later and see how ir runs. As it is, I'm convinved that with the lowering of the CO, and thus rpm falls below 1000 - the noise should revert to near normal. I did a preliminary test last night and it sure confirmed my analysis.
I hope it won't lead to anything else or I'd be the first to email you for help and directions.