Truck started running like ***** the other day. My idle is really low and when I drive it sounds like thud, thud thud sound. The faster I go the sound goes away. Could a leaky exhaust cause this problem?

 

If it sounds metallic and increases and decreases with RPM...DO NOT DRIVE IT!!!

 

That doesn't sound like a rod, maybe in the transmission? Just a guess.

 

it's more like a knock knock knock and gets louder and faster when the rpm's rise.

 

I had the same problem...very quite during start up but as the RPM's increased so did the noise and knocks. In my case it was bad main bearings at 94k miles. I since have had it rebuilt/bored and everything in the motor is new except the block. Best of all it now has a 4yr/40k mile warranty!