Another problem?
 

When i start my car and when i drive i hear a knocking noise on the right side. This doesnt happn the whole time driving just starting and like 5 minutes after.

Possibly exhaust pipe either hitting rear axle tube, rear subframe or gas tank. Once exhaust heats up and expands it moves enough that it doesn't rattle.

Only way to really find out it to crawl under there and start moving things around

Start the car up and go outside and listen to where the noise is coming from. Check for anything loose in the exhaust and check to see if the cats are shot by banging softly next to them and hearing for any rattling. My car has been rattling lately but only until it warms up and in my case, the driver side cat is shot. Is the noise closer to what something would sound like if the ehaust was getting hit by a hammer or closer to the sound of change being shaken up in a can?

The noise is more like a crackling and its closer to getting hit by a hammer.