I had a 05 Coly 2wd 3.5 5spd that was wrecked and now have a 07 4wd 3.7 and both make a Knoc,Knoc sound from under the cab part of the truck about a min. after I turn it off.It doesn't sound like anything is wrong I'm just curious about what it is,anyone know?

 

Its normal. Catalytic converter. Its just cooling down. Sounds like someones thumping on a tin bucket. All cars do it to an extent, but the newer catalytic converters are made better, so they have a lot more tapping noise than older cars.

 

Thanks, I had a feeling that's what it was and you confirmed it.