meat in smoker coming out black

looking at all the comments, people aren't describing the problem properly.  The meat is cooking fine, but somewhere in the process, a black slimy film is developing on the meat.  I have two smokers, one you can control the vents at the top and the bottom and the other, no control.  The one with no control of changing the venting, I have never had this issue.  The one where I can control the vents at the bottom and the top, the meats come out black and slimy.  Again, the actual cooking of the meats comes out great, but the black slime is quite messy when eating and part of me says this can't be healthy.  I feel it is an issue with the vents.  Partly can be the wood chip pan but still think it has something to do with the venting.  I guess I just open up the top more and let it go???  Any thoughts to this issue now remembering it has nothing to do with the done-ness or bark of the meat.