So I got a NOS pair of 2A3 tubes from a reputable seller and have an intermittent noise in 1 of the tubes. For reference, seller has already given suggestions, etc. but want to borrow SBAF collective knowledge: - Noise is usually a scratching etchy noise in a somewhat random pattern only in 1 channel, sometimes the noise resembles white noise, sometimes noise just sounds like random electronic noise, and sometimes it's a mix of the above. - Noise follows the channel for the 2A3 tube. Swapped rectifier and input tubes too just to be sure, made no difference. - 2A3 tubes measure fine - Noise was constant when tube was new, seller suspected small flake of debris on something inside, recommended firm (but not too firm) taps of glass against a table and then a few more solid taps but with the base against the table. Repeat 1 or 2 more times if needed (I did). Burn in at least 24 hours (not necessarily continuous). After doing the above, the noise is now intermittent. Noise is more likely to happen after the amp has been on for a few hours. - Noise does not change with different volume (I can even disconnect inputs, same noise). - Noise will always build up to a crescendo and then suddenly drop out. - Checked power, moved wall sockets, etc. Does the tube just need more burn in? Or is it time to return the tube?