Just a guess but that kind of sounds like the oil isn't getting to the valves fast enough. I had a 91 Jetta with TONS of kms on it and after 2 weeks of very hard driving the oil pump started to fail. I would hear loud ticking at times coming from the values because there wasnt enough oil pressure. The pump didnt completely fail but it was dieing so I had the car towed so I didnt damage the engine.
The oil is not getting to the engine at start up. There are several causes for this:
1) The oil filter "Drain back valving" is bad, causing the oil to drain out of the filter when the engine is stopped. It takes the engine a few moments to refill the filter before the oil gets up into the engine. This can happen to spin on filters. Not sure how the filter is on the V6.
2) The oil is too thick or thin. Too thick and it flows like honey in the engine, taking awhile to get up to the valves etc. Too thin may be because it lost it's lubricosity.
3) The oil pump has problems or the engine is worn out (not likely)
4) The oil level is low.
I would change out the oil and filter. I would recommend a Synthetic oil. Synthetic oil stay slippery while the engine is building up pressure. I read elsewhere on the forum that too thick of oil cause rattling on start up.