It's too fast and irregular for rod knock, from what I can make out from my seat here in my cube. I would say that Mercman's diagnosis may be spot on. In any case it wouldn't hurt to run some MOPAR Combustion Chamber Cleaner through it, which runs about $5 a can from your local Chrysler dealer. It does exactly what mercman described. It breaks up the carbon in your engine and shoots it out the exhaust.
The only variation I take from the instruction on the can are to let the car sit a least a few hours once the inter contents are emptied into the engine, to really let it do it's work. Then when you start her up you'll sweat your car was on old diesel train by the amount of smoke and noxious crap that come out the exhaust. Great for redusing the mosquito population in your area (not so great for the ozone layer!).
Ryan, call me if you have questions.
