Slight hum coming from preamp/amp

My surmise is the hum has something to do with the computer but if you only hear it with your ears near the drivers of the speaker its absolutely no concern whatsoever. 

Routing.. simple as could be, and cost nothing.. Make sure ALL the cables are separate.  If they have to cross, a 90 or close to it.  Get it off the floor.  WHY? Static E.. Pretty bad  when it's dry and windy..

Turn the Volume up mid way, BUT nothing playing...You can yo yo the cables, lift them up and down and all around.. If you hear noise.. Rout until it goes away.. Usually about 1/2 inch or so between.. Little bit higher off the floor, AY!

Make sure everything is plugged into the same plug..

Be careful with routers, and PC with their noisey power supplies... and Valves(tubes) and anything for that matter.

I have ZERO noise, I mean zip... Old tube preamps, power amps, everything under the sun. TT, routers, SACD, Blueray, Reel to Reel, OXOs, 7 enclosures, all High E speakers... NO unwanted NOISE...
40db to 120db..

Regards

Pretty true. Most electrical thingies emit some sort of acoustic noise, especially amplified by speakers. Don't worry about it. Enjoy the music

Plug your ears.
You must be living in an anechoic chamber.
Come out come out to the real world

Don’t press your ears next to the speakers!