ok.. this is what I have done. In the past after every brew I used boiling water to go though every pumps, pots, and coil right after the brew was in the fermenter. My thought was all the wort was still watery and it shouldn't dry in the coil. If I got grains in there (which i never thought I did) I would havc thought the grains would be pushed out. I also cleaned with PBW a few times in the past but not all the time.
Yesterday I ran filled my boil pot with 150 f water and good amount of PBW and ran this though the coil using a pump and catching the gunk in a hop spider. I let it sit for 30 minutes after recirclating for a while, after 30 minutes I started recirculated it again though the HERMS coil and into the boil pot, catching gunk in the hop spider, I did this twice. I got a lot and it seemed to help switching the hoses. I then used clean hot water to clean out the boil pot and filled it again with hot water to clean out the pump, hoses and the HERMs coil, which I drained the best I could. Today I did the same thing and got even more gunk. It i hard for me to beleave this was all grain flakes but it just might be. If it is not from the grains I think it is from the coil, maybe some kind of plaiting coming off from the inside. I dont remember where I got the coil but it may be just a cheap one that I am having a problem with. I have used this coil for at least 3-4 years and this has just started to do this about a month ago.