Could this be one reason tubes (and perhaps records) sound better?

Sorry, forgot to add, my system is Cary Audio SLI-80 Signature integrated, Chinook Pre-amp, Linn Sonedek LP12, audio Mirror Tubadour III Nos Tube DAC and Fritz Carbon 7 speakers. 

So what would happen if you buy a stand alone white noise generator and have it playing at low levels in the background while you listen to your system?

Seems like most of them are under $50. Maybe $200 for a deluxe version. By audiophile standards this is the cheapest tweak you can imagine

Hiss and pops and clicks and other forms of tube and record noise are not white noise.

If the signal path is absolutely clean then there would not be any need for the added white noise.  But alas ... our digital gears are full of "correlated high frequency" noise.  Some DAC intentionally have "white noise" added to mask or lessen the effect of "correlated digital noise".  

Hiss and pops and clicks and other forms of tube and record noise are not white noise

It can get complicated. To make a general statement can lead to over-simplification.  Are those "hiss", "pops", and "clicks" occurring randomly?  That's something to think about.