Why i hear rattle from chevy avalanche exhaust?

Might be Exhaust, but if Exhaust is loose , you usualy here a rattle when you are also driving the car on the road. Best to take Car to local Repairer , put Car on ramp , and take a look , as it could be something else that Rattles.

If there truly was no oil pressure it would make a horrendous rattle sound from not only the rods but especially the hydraulic valve lifters. It sounds like probably the pressure sensor or the wiring, or both are not reading correctly. The older Chevy V8's had the pressure sensor on the side of the block, under the exhaust manifold where it would just cook it and make it leak and not work right. I always kept a direct reading pressure gauge with hose and adapters in my tool box when I felt I couldn't trust the onboard gauge. Many times it proved the gauges and idiot lights wrong.

your exhaust system could be loose and rattling against the frame or other area

If the converter rattles,it has melted and deterriated inside and is not working.
You replace the converter,after you find out why it failed
It will not be the no start issue,especially broken down inside,you have less
back pressure from the exhaust.
You have a rich fuel condition,ignition problems,vacuum leaks,etc.

it sounds like the relay in the module for the heated seats that could be going nuts due to a bad wiring connection. most likely a ground.

I would have to hear it. may be the engine mounts.

If it is a tinny rattle, I would suspect a loose heat shield on or above the exhaust. When it is cool, hit the exhaust with your hand at various points until you hear the rattle. If it is a heat shield attached to the exhaust, it can be repaired with a large hose clamp placed around it.

not sure but if you don't hear fuel pump with key on have someone crank key while you pound on bottom center of gas tank that usually makes pump start so you can get it in to change fuelpump