Buzz on left channel

[Tabaia]

Hi,

I turned on the mainline today.
Left channel now has a buzz in the signal.

What I have done:
1: Changed inputs - no change
2: unplugged input - no change
3: Changed headphone outputs - Balanced out has slightly less buzz
4: Plugged into different power out lets - no change
5: Listening without feeding audio into the unit I changed the volume pots - no change in buzz, it remains constant and no change in level.
6: Changing to high impedance increases the noise up a notch.
7: had a look through the the soldering underneath, nothing was immediately obvious to me.

Right Channel is completely silent.

What would the next step be?

[Paul Birkeland]

If you tap pretty hard on the top plate, does the buzz go away?

Typically something like this is just a solder joint that isn't 100%.

[Tabaia]

Did some tapping all around the top plate as well as gently lifting the whole unit and  tapping the whole unit on the  table. no change.

[Kris]

Did you try different headphones?

[Tabaia]

yes i did try different headphones

[Kris]

Try swapping tubes too just to rule that out.

[Tabaia]

Just swapped them - no change

[Paul Birkeland]

Can you report the IA, OA, and OB voltages on both of the high current C4S boards?

[Tabaia]

Here are the voltages
C4S Board A 
IA : 260.0
OA : 219.1
OB : 135.6
C4S Board B 
IA : 255.0
OA : 218.8
OB : 130

[Paul Birkeland]

Do you hear the same noise with nothing plugged into the RCA inputs?

[Tabaia]

Yes, the hum is consistent regardless of anything being plugged in or increases in the volume pots.
There is only a change when switching between low and high impedance, high increases the  hum.

[Thermioniclife]

Clean the tube pins and if you can clean the socket receptacle's. I believe Doc B has a video regarding this.

[Tabaia]

I removed and swapped the tubes, as far as the socket goes it should be ok as it is quite new.In anycase removing and resetting the tubes made no difference.
I think the issue may be elsewhere.
Thanks for the tip though, after looking at some other posts I gained some more knowledge on tube socket cleaning.