Mine, like Kevin's, is definitely in the ROPS and it sounds as he has described. I am going to try out the silicone idea this weekend (remove the bolt - thin coat of silicone - retighten), But I'm not sure that it is coming from the bolt interface, but from the 2 sections of the ROPS bars (horizontal / vertical) rubbing together as the RTV "torques" over changes in the terrain. It doesn't take a serious bump to cause this noise - or a certain rpm/speed. Being a previous Mule owner with the one piece roll bar - it may just be something I have to get used to. But it is a bit unnerving...