Peterbilt 379 popping

I have an 06 379 cat motor with 18 speed tranny. When i ride on bumpy rode or hit a bump. I will hear one loud “bang/ pop sound” i can not find where it’s coming from. I thought it was the dash being that i just got wiper fixed and they didn’t tighten the dash all the way. Then i thought it was the stacks because they are brand new, maybe they were hitting cab. But it doesn’t look like it. Could it be something behind the dash or something on top of transmission. I know this a vague but hopefully someone has insight

 

I would hear that inside the cab? It’s loud.
Almost like someone throws a rock at the cab or window