Why Preamps Thump on Turn on

When turning on  digital I always leave on , 

then preamp ,then amplifier,

when shutting off , Amplifier then preamp, in that order is the correct way.

that thump is DC still on the line,  do you have a tube preamp ?

if so follow this sequence.

There are some amps that get an inrush of power and cause a thump some people developed relays as a solution to this.my old carvers are an example and aftermarket has a no thump circuit  for this

Interesting ...

I have an old NAD 7220PE coupled with Spectrum 208A speakers that I acquired for dorm life way back.  Powering up would also produce a rolling 50hz burp ... 

Have a Holman APT pre coupled with Odyssey Kismet amp, which are dead-silent.

Kind of miss the burp ...

I am often reminded how difficult it is to write something that others find fun and engaging. 

Agreed with audioman58.
I would always turn on the source components first, then preamp, then power amp last. And when shutting down my system I would always power off the power amp first, then preamp, then source components last. it’s dead silent, no thump.
That thump is DC still on the line like what audioman58 described above.