[mikethedruid]

You could try removing the offending grill cloth, and replace it with something like a piece of cheesecloth temporarily. Put it all back, and see if the problem goes away. If it does, then the problem was most likely the cloth. If not, then you know it is really something else... if it is the cloth, find something that looks close, but has a weave that is more open. Another thought I have had is that just MAYBE there is a sizing in the material that is clogging it. You might try washing it in warm water, letting it dry, and seeing if it is still as impermeable to air.