Although you didn't make it clear I'm going to assume that the problem only arose in one channel (when it arose). If it occurred in both channels each time this solution wouldn't apply.
I think - you've got a bummer tube, or two. The switching around solved your problem because you positioned the bummer(s) in the least sensitive location. I have identical issues with my SP10. You can stop now and go back to listening to music, but do buy a spare pair anticipating they will fail before the others. Or you can put the new pair of tubes in the most sensitive slots and rotate the tubes after removing/replacing the tubes that buzzed (probably now in the least sensitive slots).
If you have had these tubes a long time just replace them with new tubes now and bear in mind that noisy ones can be rotated into the least sensitive slots and/or just replaced individually or pair at a time when the need arrises. Nothing wrong with keeping your present tubes for spares but weed out the buzzers. What ever makes you comfortable.
Re replacement tubes. It is best to get low noise tubes, that is tubes which have been actually tested for noise. This is not routine so you have to ask for it and you will be charged for it. That is one reason why ARC's tubes typically cost more. But I buy my tubes from other vendors because typically I don't care for the tone of the tubes ARC uses in their amps and pre-amps.
Oh, FWIW, tubes hiss and/or buzz to various levels of amplitude. This may only be a big deal if it bugs you. They may last just as long as a tube that is dead quiet. Tubes that crackle and pop get replaced once I'm certain that its not associated with problems arising from contacts in the sockets.
Hope that helps a bit.
I think - you've got a bummer tube, or two. The switching around solved your problem because you positioned the bummer(s) in the least sensitive location. I have identical issues with my SP10. You can stop now and go back to listening to music, but do buy a spare pair anticipating they will fail before the others. Or you can put the new pair of tubes in the most sensitive slots and rotate the tubes after removing/replacing the tubes that buzzed (probably now in the least sensitive slots).
If you have had these tubes a long time just replace them with new tubes now and bear in mind that noisy ones can be rotated into the least sensitive slots and/or just replaced individually or pair at a time when the need arrises. Nothing wrong with keeping your present tubes for spares but weed out the buzzers. What ever makes you comfortable.
Re replacement tubes. It is best to get low noise tubes, that is tubes which have been actually tested for noise. This is not routine so you have to ask for it and you will be charged for it. That is one reason why ARC's tubes typically cost more. But I buy my tubes from other vendors because typically I don't care for the tone of the tubes ARC uses in their amps and pre-amps.
Oh, FWIW, tubes hiss and/or buzz to various levels of amplitude. This may only be a big deal if it bugs you. They may last just as long as a tube that is dead quiet. Tubes that crackle and pop get replaced once I'm certain that its not associated with problems arising from contacts in the sockets.
Hope that helps a bit.