I've made an update to the speakers. I found they were a bit wiggly on big bumps with those barrel nut standoffs. So I got shorter spacers. My other problem was the metal on metal contact of the clamp rattled a bit too. It was more like a metal pop sound when it got to really wiggling. So here's my fixes.
You can see the wore off paint from it dancing around. This is the antitheft tube.
Lay some insulating foam tape over the mating surface
It doesn't have to be all that thick
Cut out the holes for the u bolt nits
You can also see the wore off paint where the barrel nut sat on the tube.
New standoff spacer between clamp and box. You can barely see the foam tape peeking out
I had to remove the outer bits on the first tube, so I only laid the middle on the next tube.
Here's the other side finished. This shot also shows the screws I used to keep the speakers safe.
I'll head out for a drive in a bit and see how much better it works.