Turn on thump is a common phenomenon with valve amps. The solution: turn your preamp on first, then your power amp. That should fix the problem.
3 responses Add your response
By leaving the power amp on all the time, yes, you are going to hear the turn on and turn-off transient thumps of your older preamp.
Since you indicated that your amp remains turned on all the time you should look for a different preamp with a turn-on, turn-off muting circuit if this bothers you.
The woofers sucking in probably indicates a DC transient pulse... it may not be harmful, but neither is it a good thing.