Ok, so I recently bought a PC with a set of 6.5" Lake country pads and a couple of 5.5" wolfgang pads. Today I started to work on my truck using the PC for the first time in my life. I was using a polishing pad with Optimum polish and I'm noticing a problem. All of the EDU's and how-to's that I've read regarding the PC say to not apply any pressure and let the weight of the machine do he work. Well, I was doing that, but it seems that maybe the machine is too heavy for itself?? I had it on a setting of 4.5 and it was making a god awful grinding noise and seemed to only rotate and not do it's DA jigging motion. If I lifted slightly on the machine, it would quiet down and resume it's jigging, but the I wasn't geting hardly any pad contact. Well, I polished my hood, and found some spots that needed heavier cutting. So I swapped out the 6.5" polishing pad for the 5.5" light cutting pad and started to polish. And the machine didn't do the previously mentioned crap when put on it's full weight. With the 5.5" pad installed it worked like a dream!! So my question is this: What would cause the machine to not operate properly with the 6.5" pad, but work perfectly with the 5.5"?? I used the same backing plate both times, a 5" flexible one. Could it be that maybe I need the 6" counterweight?? The one installed says for use with 5" pads only. Any help would be great!!