The other day (cutting beans) my 6620 developed a rumble when I was going up a hill on a slant or should I call it along the slope. I can't narrow it down. I have taken a bar and checked as many shafts as I can get one under and I can't find one that is obviously in bad shape. On the level it is hardly noticeable but on a side hill it is a subtle deep rumble like a cylinder bearing or something. Any ideas what I might check? The bearing on the pulley side of the cylinder was new about 750 hrs ago and seems tight and is quiet and smooth when I turn it by hand with the belt and pulley off. It is a single speed cylinder. I had a shot of rain and stuff is a little green yet. I would like to get the ole girl all ready for when the weather clears up but can't seem to figure this one out. I tried greasing different things to find it the other day and that didn't make it show up either. Any one have such a problem like this before. Thanks for any idea's.