Someone on this site who is much smarter than I said that he finds, at least with SET amps, that maybe a little noise is better. I've found this to be true with my amp. When I'm able to dial out the slight ambient hum with tube choice and other methods the amp sounds a bit constricted. No idea why. Just my experience.
There are not many smart people on this site. Some of the threads recently have dumbed down everyone.
If you take an amp or preamp using 45 valve, try rolling EML mesh 45 and the solid plate. The mesh is much noisier, the solid plate has lower noise floor. The mesh sounds airier on vocals, the solid plate just shows more music that helps inflections of instruments, which the mesh glosses over.
Moving from psvane to KR 211 reduced noise floor, plus improved other dimensions..