Tube preamp noise

I don't think I've ever had a 6SN7 (or many other types) that are not microphonic to one degree or another. Unless the problem is severe it doesn't indicate that the tube is not performing well in other respects or that the tube will fail prematurely. Minimize it with tube dampers & decouple the component from the rack. If slightly microphonic NOS tubes sound better than Chinese, then use them!

I could not notice any microphonic problem with the new Chinese tubes. I have 10 used 6SN7 GT/GTA/GTB tubes form GE, Sylvania, and EH, and they all suffer microphonic rather severely. With a gentle touch on the amp case will generate an echo on the speaker. Gentle footstep near the amp does the same thing.
I just ordered tube dampers, and I will see how much they would reduce the problem. The Chinese tubes produced rather flat sound. I will see if they will make any difference after several days. I would rather use the old tubes than the Chinese tubes if the microphonic problem is lessened or if the Chinese tubes do not improve considerably over time.

I also ordered NOS Sylvania GTB tubes with green label and chrome tops, and will see how they would do.

A simple way to isolate from rack noise or foot-falls is to float the component on a partially inflated inner tube made for a child's bike.

I got NOS Sylvania GTB tubes and 1960's Russian tubes. They sound equally good, but got Russian tubes at the same price as Chinese ones, much cheaper than Sylvania tubes. Sounds notably better than the Chinese.

For the microphonic noise, the Russian tubes are much quieter. No more foot step echos. The Sylvania tubes are still prone to some noise, even though they are less noisy than the old tubes came with the preamp.

I would highly recommend those 60's Russian made 6SN7s.