97 vr6, loud top end?

My 97 VR6 has approx. 140K. runs well, however the top end (cam area) has gotten very loud (knocking/scraping) sound like marbles inside. The cars fan seized this summer during a trip, could not stop in traffic, and got very hot, but did not overheat (boil over) However I think it got too hot and did damage. It sounds to me as if there may be something wrong in the timing chain area possibly, its hard to tell? I cannot figure our where the knock would be comming from in the cam shaft area? It has got to the point where I think something is going to fail and blow the engine. Do the cam chains in these engines require changing? Older v8 chevys would get loose and wear a hole in the timing chain cover. It looks like a lot of work to get at the cams and chain (s) area on this engine for exploritory purposes. Any help or suggestions are greatly appreciated. :banghead:

Muzzym

this deff sounds like cam chain and adjuster noise. common on older (hi mileage) vr6 engines. VW doesnt have any reccomendations on replacing chains and tensioners. Pretty much when they make noise replace them. sounds more like the upper chain adjuster is bad , more common than lower one. To replace the chains/tensioners its a major job that includes removing the transmission and intake manifold/valve cover.