Slight Tube 'Whistle' - Help?

Hi. Two Questions on my preamp:

1. Someone asked me if the pre is "hard on tubes"...what does this mean?

The EH stock tubes became super-hissy after 800 hours...stock replacements on the way. Meanwhile, i put in Amperex 6922 US PQ White labels...better in every way. Silent...until just recently. After about 300 hours with the Amperexes, i now [occassionally] hear the teeniest, tiniest bit of "whistle" thru the R tweeter only. In general, the hiss is super, super quiet (and i have 95 db speakers)...but [sometimes not always] it has gone from effectively silent to a soft whisper now in both channels.

Can a preamp be 'hard on tubes'...and if so, is there anything one can do? Or is the 'teeny R-channel whistle' a symptom of this or something else...or just par for the course with any preamp...particularly one with a ridiculously low noise floor? i cannot get over how much super-soft detailing i can now hear thru ordinary recordings.

2. In trying to figure this out, with the unit on, i tapped each tube out of curiosity...and discovered i could loudly hear it thru each speaker. Is this normal? Should i care since i dont tap my tubes while i listen?

Other than the teeniest, tiniest bit of hiss and this occassional 'whistle', the unit is dead silent...so perhaps this 'tapping' business is a non-issue?? The tube sockets themselves are on their own floating suspension systems underneath in the unit apparently.

If i put an EAT tube damper on each tube, should this stop it? Again, should i care?...is this normal?

Thanks for any guidance!!!!!!!!!