Question on tube noises

After a couple of weeks with what is a completely new system I'm beginning to get past some of the awe it initially inspired and into some of the more esoteric "annoyances." The pre-amp is a Sonic Frontiers Line 1 with stock tubes. As expected there is some very minor tube hiss. I can only hear it by placing my ear close to the speaker when there is no input and it doesn't seem to be effected by volume. My understanding is this is normal. What is of concern is that in one channel the sound is contant and uninterupted. In the other is there is some minor crackling and popping. Is this normal or is that a sign of a bad tube? Comments on when others replace tubes would also be appreciated.
Allow me to answer my own question. A tube in the DAC went out last night. It was apparently the cause of the popping and crackling. In fact, that is all it does now...
Boy, that was a quick solution :( You gotta take the good with the bad when it comes to tubes. For myself, I like their sound far too much....
The DAC was bought second hand and appears to have the original tubes. It was already in the plan to replace the DAC's tubes soon, not to mention it's a cheap undertaking even with good NOS' (they're 12AX7s). There's a local audiophile shop that specializes in tubes that has a selection on hand, so I should be back online today. In any event you are right about tubes and their sound.
We have an SAE X100 Class A Solid State Amplifier which have been "Butchered" by an inept repairman. We would like to restore this amplifier for use as a reference unit. Does anybody have a manual available for this make and model to help in the resoration. Please contact