I just replaced the timing belt, idlers, and water pump in my 3.4L on Sunday -- took about 4 hours.

The only moving parts behind the plastic timing belt cover are the cams/sprockets, water pump, crank/sprocket, and the two timing belt idler pulleys.

Since your noise is still there, I'd guess it's either the water pump or one of the idlers. You can get the belt, both idlers, tensioner, and water pump on Ebay for about $200. As I just did with mine, I'd suggest you break down and replace everything while you've got it apart.