OK, I know the knock won't hurt, but it's starting to drive me nuts (an engine shouldn't sound this way). My 2001 540iT is quiet as a church mouse when started cold but once totally warmed up has a knock that sounds just like it is a rod coming loose except that it is up high in the front of the heads.

My question = If I decide that I can't stand it anymore, what am I looking at replacing and is it something I can reasonably do myself or does it need to go to a pro or the dealer. Also rough idea on cost ? Car has 95k on it, runs great and is fast as hell, overall well maintained and in great shape. Currently using 0w40 Mobil One. Should I go to a different weight / type of oil ?? Considering going to 15w50 Mobil One as that was what I used in my 944 Turbo S and it loved it (200k and never had head off or turbo replaced).

Ideas / opinions from the vast knowledge base of the group here are welcome and solicited. I truly love the car but this noise has gotta go .

Thanks in advance, Vaughan