Pretty much all tubes are microphonic, some more some less. Even high end manufacturers seem to delight in placing tube sockets in the middle of a PC board drum head.

Tube Sox work well, probably the silcone rings will work. The trouble with the pencil tap method is that you don't get to find that one frequency where the whole PCB resonates. I had problems with a resonance that sounded like a wolf note at around the mid 30 Hetrz range. Some records developed extraordinary bass levels and when the volume was turned up a little more the notes never stopped - oops.

I ended up trying many absorbant feet (cones wont help unless the shelf the unit is sitting on is dead quiet) dampning the shelf and then even appying that stick on damping material to the inside top and bottom covers on my pre-amp (with vents to let heat out).

In my case the real culprit was that pretty Oak entertainment system that I needed to overcome the wife factor.

It is safe and recommended by me to overdo any vibration fix, increased bass clarity for relatively small amounts of money will be your reward.