Hi Scott, beautiful pics!
When you say "shunt," it seems you're talking about noise? (Shunt is an electrical term.)
The amount of noise from your coupler is very dependent on the level & condition of brake fluid in your trailer's brake system. If your fluid level is low or your brake lines have air in them, the coupler will slide farther with each stop & start, even to the point of the brakes no longer working.
Pop that large black plastic cap off. Under that you'll find a large plastic screw-in cap. That's the opening of the master cylinder. Make sure your brake fluid is up at the right level. Whether it is or not, consider bleeding your trailer's brakes. That's something that ought to be done every couple of years anyway. It gets any air out that might be in your lines, and gradually replaces the old fluid with new (brake fluid naturally attracts and absorbs moisture which reduces it's effectiveness).
Of course, all this assumes there's nothing loose or broken on your truck's hitch

.