Reduce hum on reverb - new 6G16 build

[Medley]

Hi again, all.

Well, I've completed the build of my 63 Vibroverb clone. It's a beautiful amp and sounds killer with my Gretsch G6228. I do have some noise I'd like to minimize as much as possible, but I understand some is more or less accepted with these amps.
The primary issue I'd like to solicit help with is some hum that is proportional to the reverb dwell setting. It is unaffected by the volume knob on the bright channel, of course, and seems to be 120hz. This is with the tank plugged in. If I disconnect the tank, the noise is much gnarlier and seems to be louder and also a combination 60 and 120hz hum and buzz salad. I'll include a hi-res picture so you can see how the wires are run. I haven't done any trouble shooting other than replacing the 12ax7 in v3 with a 5751, and that just to tame the rate of gain at the knob a little. But the hum remains. It's not so loud as to be unusable, and in fact with the reverb knob at about 3 it is very usable at bedroom levels; I could probably gig with it in a noisy club and nobody would notice, but I'd like to reduce the noise floor if possible. I haven't yet swapped out the JJ 12ax7 in v4, but I do have a decent NOS replacement I could try in there. I just don't think that's the most likely culprit.
Of course, when the tremolo is engaged it ampliflies the mild hiss that is present there and I attribute the most likely cause of that to the presence of carbon comp resistors. Is there one in particular I might consider swapping out for a metal film that might reduce this?
Any wisdom or observations you can share would be appreciated.
Picture, as promised...

[sluckey]

If you ground V4 pin 2 does the hum go away?
I would put the 12AX7 back in V3 socket and put the 5751 in the V4 socket.

[Medley]

If you ground V4 pin 2 does the hum go away?
I would put the 12AX7 back in V3 socket and put the 5751 in the V4 socket.

I will have to remove the chassis from the cabinet and put it back on my bench, but will definitely try both of your suggestions and report back. Thanks.

[sluckey]

Probably need to leave the chassis on the bench while we are trying to help.

[Medley]

Agreed. Was anxious to get the thing together and playing, but I do have a few things to tidy up besides the unwanted noise, so will bring it back downstairs and pull the chassis to finish up.

Don't know if you noticed the kludged ground resistor thing on the negative side of the board where the LTP is grounded. Mojotone missed including the 470R grounding resistor in the kit, so I had to come up with my own to get it working and finished: two 800R in parallel and two 100R parallel, then wired in series for 454R while I waited for the proper 470R to come in the mail. I have it now, from them, so want to put that in place as well. There were several parts missing from this kit that I've had to go back to them to replace. If I order the part myself I have to pay $20 flat fee shipping from Mouser, so got Mojotone to replace the part and pay for the shipping.

I'll post an update once I try out your suggestions.