Tube preamp noise question

I have a question for experienced tube preamp users. I purchased my first tube component, a preamp, a few months ago and am having a noise issue. It uses 5881 and 6SN7 tubes for their respective functions. I have not yet contacted the manufacturer because I wanted to sort out the issue myself if possible. The noise I hear is somewhat like the crackle and pop of a scratched LP. Sometimes, it could also be described as like the “roar” of a natural/propane gas flame (e.g. Bunsen burner), and sometimes it sounds like “squeaking” of Styrofoam rubbing, etc. It comes and goes and does not seem to go away as the tubes warm up. At first it was only in my left channel so I swapped the tubes from L to R but the noise remained in the L channel. My thinking at that point was that it wasn’t tube related and must be something in the electronics of the pre. After a month or so, now the same of noise is appearing in the right channel as well. The noise is not subtle and can easily be heard while music or a movie is playing. It’s embarrassing when having friend over as well.

My question is what may be causing this? My speakers are sensitive (95 db/w) so not sure this could just be tube rush because of the volume and intermittent nature, but I'm not familiar with tubes enough to rule that out. Is it a case of noisy tubes that I can replace or should I be concerned about the innards of the component? I appreciate any insight and thoughts you may have.
I am confused. While your problem sounds like a weak set of tubes, are you sure you are talking about a pre-amp? I believe that the 5881 is a pentode power tube used in amplifiers. If you would, exactly what make and model equipment are you refering to?
On further thought, my suspicion is the 6sn7's are weak or need replacing. If you have a tester, test, but I suppose you don't, so you will need to find someone locally who does (local TV repair shop). The alternative is to buy a new batch of 6sn7's and see how they work out.
The sounds you are describing definitely sound like the tubes are bad. I would try all new tubes. If you are lucky enough to have an audio buddy with some tube spares, maybe you can try them. PS: what is your amplifier?
The basic tube of each tube type you have may be worth pricing
to see if you can try a new set of one or the other or a set of both. Did you reverse left/right with both the 5881's and
the 6SN7's. If you bought the unit new, I would obviously
contact the dealer. If not, you may want to get your hands on
a set of maybe the 6SN7's and try them first. However, you may
be surprised at the customer service certain companies may
offer even if it is used. IMO, it can only benefit them and
would certainly boost their reputation at the very least.
What is the preamp brand and model?
I would say you have some bad microphonic tubes. I also have 6sn7 tubes and they will, can, become unstable from one day to the next. Also, the other day I left my music playing while I ran on an errand...when I got back I saw that my cd player was still going but there was no sound from my system. After analyzing for a few minutes I noticed that my 5aw4 tube in the pream0p was completely cold. Sometimes the cold solder wire connection between the inner tube and the tube pins will simply seperate. I guess what I am trying to say is that all tube lovers are masochists...just kidding! Anyway, I think new tubes will resolve your problem.
welcome to tubes! the good news is that a lot of issues that will come up simply involve replacing tubes. you need to know which tubes do what (L or R, phono or line, etc. - do you have the user's manual?), then start using logical deduction to figure out where the problem tube is. e.g. is the noise on both channels? is it phono only or all inputs? having a spare set of pretty much any tubes you use is definitely worthwhile. not a bad idea to keep a log of what tubes you've changed out and when...

p.s.turn off the power when taking out tubes!
Another possibility you might consider is dirty tube sockets, particularly on older tube gear. Parts Connexion offers slender nylon brushes that can be used to clean tube sockets. A fine brass brush can be used to clean tube pins as well. Sometimes crackling noises in tube gear are solely due to poor or erratic connections to the tubes.

Thanks everyone for the responses. It sounds like the consensus is that it is tube related. I'll report back with my results.
Gjames, if the sound appears only in one channel, the first thing I would do would be to swap the interconnects from the preamp to amp, left for right *at the amp input only*.

See if the problem moves. If it does not--> amp
if it does --> preamp

The compalint sounds like a microphonic tube, and swapping it did nothing, but what if it was in the amp?
As promised, I have an update to the original post. The problem was in the 6SN7 tubes. Thanks to McFarland who graciously supplied me with some spares that he had on hand, I replaced the stock tubes and voila, no more of the noise that was present before. Thanks to all who responded and pointed me in the right direction and most of all to Mcfarland for supplying the replacements. Now I'm off to find some good NOS 6SN7s to take up permanent residence.
If you're looking for very quiet NOS 6SN7 tubes check with either Andy at Vintage Tube Services or Audiogon member Whoopadeedoo. You won't be disappointed.
I thought Andy had closed up shop?
Just visited Andy's website so I was misinformed about him closing up shop. Thanks for the tip.
I think he's been contemplating it as I have heard similar news. I'm glad he's still around though. One of the good guys in audio and the best in tubes IMO.