That is a worrying noise. I would take off the rocker cover and see if you can get any slack on the timing chain. If it was a tensioner (assuming it's an oil pressure regulated unit) the sound would go away to some extent when the engine is up to operating pressure. If the timing chain has done a lot of work I would be inclined to pull the engine out and replace everything. I've heard of the impellor shearing off the end of the water pump internals. It will squeal like a pig and your engine temp will sky rocket - you'll know straight away what's happened if it fails.