My Ultimate drivers backrest squeaked in the slab-post mount. I took a thin tight wrap with electrical tape on the post. That stopped the squeak, but the tape kind of melted and ran over time and I about had to use a chain fall to yank the bastard out of the seat slot. So I cleaned that mess off, and am not doing it again.

I think a little Vaseline or grease on the seat base bumpers may stop the seat squeaks, for a while.
If you have riding music, turn it up and the squeaks disappear.

(Or cobra pipes)
I had a mouse nest in my Vtwin intake/air cleaner. It didn't squeak, but boy did it smell nasty after the first spring ride BBQ. Poor little feller.