A small tick is normal when the mute relays open and close, at turn on and turn off, but a loud pop is definitely not normal...
Please try disconnecting the interconnect from the suspect 7B, switch it to the balanced/xlr input, and try power cycling it again. If the noise persists, I would suggest sending it to us for warranty service.
If the noise is now gone, the preamp may be passing a small amount of offset, resulting in the noise.
Thanks,
Mike