Speakers low pitch humming, is it normal, or real issue with preamp?

Could be a ground loop.  You could try using a cheater plug to lift the ground on the preamp, amp, etc. and see if that eliminates the hum.  Not a long-term solution but at least you’ll see if that’s the problem and then go from there.  I suppose you could also try adjusting the positions of your power cables if certain ones are crossed — not likely the source of the problem but it’s free and good to rule out.  Just a couple thoughts FWIW, and best of luck in tracking down the problem. 

I agree with @soix could be a ground loop.  I would try his solution and see if that eliminates the issue.  If it does, try plugging the pre into an outlet on a different house circuit.  

If you can only hear it from a few inches away I wouldn’t worry about it. The only setup I ever had that was Completely silent was a Lyngdorf integrated. If you sit in the quiet room and really listen and can hear something then that’s a different story. 

I can hear the hissing and humming noise when I keep my ears close to speakers, so is it normal that any preamp will produce this kind of noise (even without any input cable)? Or is it an issue with my item? Sorry I am a perfectionist.

Unplug video sources going into the C53.  Unplug their AC connections and start there.   If you are using the eArc on the DA2 start there it may a ground loop between the TV

Its unlikely a bad component,  its noise and you just have to pinpoint it

I can hear the hissing and humming noise when I keep my ears close to speakers, so is it normal that any preamp will produce this kind of noise (even without any input cable)? Or is it an issue with my item? Sorry I am a perfectionist.

Completely normal. Has to do with the minimum gain on the preamp, your amp sensitivity, and your speakers. I would not change anything but you can put a pad on your preamp cables and that will knock it down. I also keep a pair of attenuators around just for this problem.

Hoorays!! It’s all your inputs and inspirations! Some valuable lesson learnt: I started to set up the components all over again (without much hope), unplugged everything, and plug in the cables (and compare different cables and inputs) one by one, finally I find the problem: my most trusted Audioquest balanced cable from preamp to amp was the cause of humming! I changed it with the much cheaper wbc and problem was solved! It’s always something minor that screws up the whole plan! I am a happy music audience now!

Excellent 

Resolved. 
 

Congratulations!

CU AQ

Make sure all your gears plugged into one circuit. Get a filter for your tv cable cord, try disconnecting Cable to see if that does anything.

Don’t sit so close to the speaker. Buy a puppy. Make a chocolate milkshake.

I definitely think you're too nervous and should try pharmaceuticals