Ouch, that sounds pretty nasty, I would get that looked at as soon as possible. I recently had my chain tensioner paddles replaced, since my car was already in the shop getting an IMS retrofit kit, clutch, and RMS installed. About a week or two before I took it in, it developed a somewhat similar sound upon cold starts, though not as profound and only lasting about 1-1.5 seconds. Here is photo of the chain tensioner paddles that were replaced, as you can see the two inner paddles on both banks (the two on the left side of the photo) were pretty ate up and I was told that this was the cause of the noise I heard. The link below, is to a thread I started prior to taking it into the shop, regarding my concerns of a potential IMS failure, after discovering metal flakes in my oil filter.
Metal Flakes Found in Oil Filter