U lock rattle

First an update:

I junked the cantilevers on my trek 820 for v brakes and levers. BTW,
I had to modify the little steel brake cable tube that was brazed to
the frame behind the seat tube. I removed about 3/4 of it with a
grinder. I am very pleased with the performance now.

The new issue:

I got a U lock with it and it rattles like a mother when Im riding.
Is there any little things I can do to prevent all of the noise
eminating from the lock? Thanks.