Tube Pre amp noise

I just purchased a used tube pre amp and notice a hiss, snap crackle and pop comming from the tweeters. Speakers B&W 801 matrix 11's. No noise at all when I plug my Bryston into the system..anyways, two sets of brand new tubes were tried and still the exact same noise comming from the tweeters. Two 12AU7 and two 12AT7 tubes used in this pre. If I turn the gain up on the preamp the noise does not increae in volume. It will play music that sounds OK. Just this hiss, snap crackle pop at low level is unacceptable..Any ideas what may be causing this noise?
It certainly sounds like the tube preamp, but audible hiss is frequently from noisy tubes which you have ruled out. A tube preamp may have some low level hiss, I don't know what you can tolerate. Crackles and pops are never normal and thus the pre needs to be checked out.
I've noticed that tube preamps are also more sensitive to grounding issues and interconnect mechanical issues than solid state preamps. So you may try using a cheater plug on the preamps power cord to determine if you have a grounding issue and make sure that any locking RCA barrels are tightened.

Once I tried changing tubes several times and couldn't get my tube preamp to quiet down. Turns out all I had to do was to tighten the locking RCA jacks and the noise disappeared. It's worth the effort though, because tube preamps are more sensitive to the musical signal too.

If the noise still persists, then the preamp should be serviced.
Two cause; if the noise is variable, it is in the gain stage and may not be a tube, especially if it is both channels. I doubt both tubes went bad. But, you say it is constant.

It sounds like the noise is after the gain stage since it is constant volume superimposed on the signal. That would tell me it is a final output tube(s). If it is ONE channel, switch the two output tubes to verify the noise changes channels / follows the tube. Or, did the noiser tube change sides?

If it is thermal shot noise or plate grid voltage noise that you hear it won't amplify. Be sure you know which tubes are in the final output stage (past the volume control).

Experts are here to help if you give the model number of your pre amplifier. And, the manufacturer can quicky identify your problem in short order if it is a tube issues and not the high-voltage stage driving the tubes (that will need service).

Well a lot late in replying, but the NEW tubes I installed (JJ) were suspect as I installed nos telefunkens and the noise is gone. Amperex tubes installed (rolling) and no noise as well. Thanks for the info, appreciated D.