I had a shopping bag blow on to mine right after i parked and went into a store. It was pretty thick. I used a brand new utility knife blade, and very lightly, very carefully scraped it off with the pipes completely cold. I did not notice it for a few days because it was towards the bottom half of the muffler but it came off fairly easy when the pipe was cool. I wonder if the hole is some kind of drain to prevent rusting. I agree a picture would be helpful.
