I have a Trek 4100 with an Altus rear derailleur. I recently spent some time trail riding and consequently plowing through some deep mud - almost up to the bottom bracket! After I was out of the muddy section I notice my chain was making a lot of noise on the down stroke while pedaling hard. I later cleaned up my drive train and re-oiled with Tri-Flow, but the noise stayed. I've adjusted the rear derailleur as shown in my repair manual, but I just can't get it to quiet down. It shifts like a dream - no skipping, no mis-shifts, etc.... Could I have twisted the cage or otherwise damaged the derailleur just by going through the mud? Please help!!