Thanks for everyone who has responded to my post. This is what I will
do in the coming spring (I have already parked the boat for the
winter):
- Add tape around the steel pin in the class-3 hitch to ease the
metal-to-metal contact and see if the noise will go away. If not...
- Add grease to the hitch grease points and see if the noise will
go away. If not...
- Bring the trailer to a brake shop.

Thanks!

Jay Chan