I had the same problem with the hitch receiver on a Jeep Cherokee.  The ball
mount tube would flap up and down as the Jeep and trailer would drive over
bumps.

The ball mount tube had a VERY sloppy fit into the receiver tube.   The
outboard end of my receiver tube had a reinforcing strap, 1" wide X 1/2"
thick, wrapped around the opening and welded to the tube.  This strap kept
the end of the receiver tube from enlarging, funnel shaped, under load.

I solved the up & down movement and pin slop by drilling a hole DOWN through
the top of the receiver tube and reinforcing strap.  I then tapped the hole
for a 1/2" X 20 bolt.  If your hitch receiver tube does not have a wide
strap wrapped around the end, you could have a steel nut welded to the top
of the tube.

When hitching up, I inserted the ball mount tube into the receiver tube and
tightened the 1/2" X 20 bolt down onto the ball mount tube with a Crescent
wrench.

That took all of the vertical movement and pin slop out of the connection.
It was quiet after that.

Try it....  It worked for me.

Good Luck.

Tim