Loud vaule chatter

There's not many options when it is the valves, you can try some oil additive remedies but eventually you're looking at some head work. This is the point when you think to yourself how much dual overhead cams suck if only because they make pulling heads such a PITA. Gone are the days of simply pulling a head for some machine work and new valve seats quick and easy. If I can suggest anything, pull your valve covers and give it a listen and poke around and determine exactly what is making the noise before making any big $$ decisions. If you like the car and want to keep it for another 100K miles, pull the heads, send them out for a rebuild, and replace the timing chains. If you're not up to the task of remounting them, look up some mobile mechanics in your area who can get your timing chain and heads back on in the comfort of your garage. That's a cheap way to do this...

I'd pull the oil pan and check to see if the pickup screen is clogged. Also part of the oil filter could have got out of the filter and clogged an oil passage. Sound like you have a lubrication problem to me.