I know the white smoke would be caused by coolant, which would be leaking into the combustion chamber.
Exhaust of an engine is a gas.
Are you referring to a loud exhaust sound? If so, it could be (Going from the engine back to the tailpipe) a cracked or leaking exhaust manifold - a leaking exhaust pipe - a leaking catalytic converter - a leaking muffler. That covers the exhaust system. If you are talking about a noisy clattering sound in the engine, you could possibly need a valve adjustment.
possibly the exhaust has a hole in it allowing the emmissions water which normal runs out of the tail pipe to run out rusted hole in muffler or exhaust pipe system. Does your truck bed have water in it from a recent rain storm ? The only other thing back there is the gas tank itself, but you would smell gas if that is leaking in liquid form.
If its smells like gas, you are putting too much gas in the engine and some is unburnt and going out the exhaust. Exhaust underneath means there is a leak in the system somewhere. If there is no louder noise or hissing, I would expect the catalytic converter is leaking. Have it checked and get a tune up. http://www.autozone.com/servlet/UiBroker?UseCase=S001&UserAction=viewSimpleDiagInfo&Parameters=info answer bad exhaust pipe
leaking past the rings
The exhaust pipe was leaking.
Because the truck is leaking silly if u smell gas why u driving its leaking
Leaking valve cover gaskets would leak onto the exhaust pipes under the hood of the car.
you must have air leaking into the exhaust system that will cause backfire when you decelerate raw gas goes into the system
Remove toxic
I would check the Flange gasket. It is the gasket that sits between your exaust manifold and your exaust pipes