Expanding questions about tubes in a preamp

Hello to all...

Started with a (helpful) discussion titled "How to select tubes for a line level preamp"... Expanding questions that have generated from that...

Have learned that hum/noise from tubes is a major consideration - now trying to figure cheap ways to address quieting the 12AX7s and the EF86s.

Would like to try "banding" the tubes with rubber ring washers - one?two?three per tube?

Where should the rings be on the tube: Top? Mid? Bot?

Can you over dampen a tube?

Knowledgeable tube users/ Masters input/suggestions please...