Could be the tubes and the tube sockets to start with. If that is not the case could be the volume control. RCA cable connections? Then a cap of resistor. If in the NYC area I can take a look at it once you have eliminated the above.
Hybrid Tube Preamp - Loud Pops and Crackles
My stalwart VTL 7.5 iii pre is broadcasting loud pops and crackles through my speakers, scaring me about damage to the speakers. First, I thought my aged 12au7 NOS 7316's tubes were dying, so I replaced them with NOS Amperex Bugle Boys. The pre started with the loud pops and crackles again.
Are both of these tubes dying, or is the problem with the pre itself? Any thoughts? Thank you. Neal