I have a question about a low level sound that comes off the 5U4's that I have in my CSP2. I have the CSP at my table next to the flat screen monitor but away from any interference that I can see. I run line level about 20 feet through broadcast standard low capacitance Belden 1505F interconnects. This has worked well for me as the control over the computer volume and CSP at the chair is very nice to have. As I sit between low level passages or between songs there is a tinkling ringy sound out of the rectifier that I have heard before but never worried about until the unit now sits right next to me. It sounds like the filaments ringing in a light bulb. If your ear is pointed just right it can be detected across the room. It is a very faint sound most of the time unless your ear is pointed at the preamp. The only way to stop it momentarily is to tap flick or nudge the tube but it starts back a short while after. I run straight bottle RCA/GE black plate double DD top getters or side getters. The plate structure is all the same on these I will try the Ruby's that Steve sends with the equipment but I really like the sound of 50's 60's black plate 5U4GB. Just the best I've put in the CSP so far.
This ringing sound does not seem to impart any noise or hum to the output of the preamp.

Is this just a niggling issue with certain rectifiers or is it common among 5U4 types like these? Anyone having heard this phenom. let me know.

PS just tapped the tube while it was quiet and the damn thing started the tinkling noise again. Dumb thing