Popping sound on rear while trailer is getting loaded

Just curious, bought an Intl 9400 (2001). once I'm backed into the dock, with the truck off (This is my first stop of the day so the trailer is almost empty), the forklift driver must come to the front of the trailer and I noticed it presses down on the rear of my truck, causing a popping sound to come from somewhere. My thought was that its a u bolt that needs replacing or the shocks maybe, air bags will hold air for almost 2 days when the trucks just sitting at the yard, so I'm pretty sure those are not the problem. Leaf springs look good, none missing. Just wondering if I should be concerned a about this popping sound. Driven many other company trucks with various sounds but this one is my own so I'm trying to stay on top of things.

 

That makes sense, brakes are new. I know the truck needs some shocks cause it's like riding a #### horse at times goin down the road. Thanks for your input Keith, I'm kinda hypochondriac as a new owner op lol

 

The trucks currently at the company yard but I am going to go look at it n see if they are missing. The steering shaft is getting looked at next week, not pleased with the play & movement. Besides the complaints I mentioned I'm pretty happy with it, it's a local 300 mi a day hauler