Never seen this before.....
Over the last couple years, my car has seemed to be "jumping" timing. I've done a few things trying to figure out the issue, but just recently decided to buy a new timing chain tensioner. I just started to check things out on the car, and when I took the valve cover off I noticed this. Somehow, at sometime the chain is getting loose enough to slap the damn valve cover lol. As it sits the chain is tight, so I'm not sure what the deal is. I'm going to get everything timing related back to where it should be, put the new tensioner(thanks GregV!) in and see how it goes afterward.