It only happens after I drive the car around for a lil bit and it does it when I'm going straight or turning and gets louder when I accelerate and it sounds like it's coming from center underneath the car
The sound doesn't happen if the car just sits warms up and u rev it and turn the wheels. The sound only happens when I'm driving and after 10 mins of driving this knocking noise starts happening. And I don't have ac in the car
This one's gonna be tough.
Start with the exhaust, metal expands when heated, but you knew that already, with that in mind, talk it for a ride and when the noise starts take it to the house and jack up the rear end, use jack stands of course, we can't have members get'n squished, start it up and put it in gear see if it rattles, check exhaust connections and hangers, then the drive shaft, trans mount things like that.
Let us know what you find or don't find.
Haven't found out the issue yet but I just found a 1/2" pipe going along the exhaust pipe and sitting up against the catalytic converter so that might be getting hit up against it making the noise I do not know
I would put it on jacks and grab a pry bar and touch/push on exhaust to rule it out (from headers to the end of the h-pipe). But, since it does it at idle/not moving, I think Real time is on to something.
Also, check your transmission mount and engine mounts.