My Dakota has 146 K on the 3.9. The motor runs real good, but has a little rattle type sound at low rpm's. It's not a knock & sounds like it's near the front of the motor. Once it's reved, it seems to go away. What could it be?
Drove truck tonight. The drive belt has started squeaking, even at idle. Drove it about 20 miles & sounds like maybe one of the belt idler pulleys is bad. After driving at 55 mph, for say 8-10 miles, the belt sometimes makes a terrible noise. Like a pulley is trying to stop & the belt is still going. Can also hear what sounds like a bearing squial at the same time. After slowing down, it doesn't do it very much. I'll check that in the morning. The slight rattle is still there, so I'll order a timing chain for that.
Sounds like your other noise may be a bad belt, water pump, or a pulley. Tensioner could be weak also. You are gonna have the water pump off anyway to change the t-chain & tensioner, you might as well replace it.
UPDATES: Just yesterday (1/30) I replaced the timing chain & added a new tensioner. The rattle is gone. Truck has 146K on it & I don't think it had ever been replaced. Chain was worn out worse than any I had ever seen. Also installed a new idler pulley & belt. Truck is running better than ever now.