Preamp "Snap, Crackle, Pop"

I recently purchased an Antique Sound USA PA-5 preamp from a fellow A-gon user. I have been enjoying it, and love the sound; however, I recently started hearing some disturbing amounts of noise during playback of quite passages. The preamp uses 12AX7s and 12AU7s for each input and a GZ34 for the output. I have tested with another preamp and heard no noise, so I ruled out my Amplifier (Jolida JD-502P). I'm fairly certain the problem exists on the output, because I tested the preamp by switching inputs at full volume (it was only a test!) and heard the same snap, crackle, and pop on each input. When it was sold to me, I was told the phono input had this issue, but since purchasing, each input has developed this disappointing "feature".
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I should also mention that there is a tremendous amount of hissing and feedback at times as well. I hope someone has input, I'm just not certain which route to go. New tubes? Output caps? It was made in 1997, and still has all but one original tubes, do you think they are end-of-life?
End of life is a good description of the unit. Best to dump it and not put any money into its tubes etc. Otherwise it will drive you crazy, leaving you little time to 'enjoy the music'.
It probably just needs new tubes. I would bet that if you contacted Antique Sound Labs they could help you diagnose and find a solution.
I would agree with Dan_ed about probably needing new tubes. That is what it sounds like to me. I would start there before you even consider dumping the unit.
I agree with the previous two posters concerning replacing the tubes.

Hi all,

Thanks for the suggestions, but I think I found the problem. I'm certainly going to re-tube this guy soon, as some new 12AX7s to replace the 12AU7s would be a good idea anyways.

The tube socket for the GZ34 was the culprit (at least upon initial listening after the fix). The half-sleeves that contact the pins had been spread apart and split over the years, and as the preamp heated, this caused the contacts to spread even farther apart, and were making insufficient contact with the tube.

Buconero117: I won't be "dumping" it because I spent hard-earned cash on it and enjoy vintage gear. Fifty dollars in tubes would be far cheaper than a new preamp. I respect the opinion, but not posting at all would have been more help.
This company might not have ties to the present Antique Sound Labs company. They (ASUSA) advertised as a USA product I think. I had an amp of theirs years back. The tubes would be the first place to look for sure. But, coupling caps, or the power supply caps could be starting to go too. I have a couple of over 50 year old pieces of gear that are stock, and still going good. A lot of the old gear just keeps going up in value.