Twofold noise issue!

[Immo]

I need help from someone who's a "maestro" of electronics. Strap yourselves in and try to keep up with the story, I shall share all the details. I "color-coded" all the electronics issues I had with the bass so it'll be clearer.

My TwinSplit bass guitar has, well, two split coil pickups. I bought a stock Encore bass, having a second split coil form a same bass model laying around. So I decided to build a P-P-Bass, wired like a Jazz Bass.
Once all was wired, the innards looked like this:

When plugged, there was no hum. However, when two pickups were set at the same volume, there was a strong comb filtering-like effect, basically, the lows vanished and it sounded out of phase. I did some research and found out the way to fix it was to switch hot and ground outputs of one of the pickups. While I was tinkering, I also added a treble bleed mod to the south pickup's volume pot - after all, the south pickup was there to deliver treble! So, after the mod was done, the innards looked like this:

Now the both pickups set on the same volume had full-bodied sound. However, after a while - not sure when exactly -  a hum issue with the North one appeared. Either solo or paired, it hummed like a badly shielded pickup. I thought it's due to bad shielding the bass has. Due to various personal issues and the fact the hum wasn't that horrible, I always promised myself to fix it "the next day". I always thought it is a shielding issue. Only today, after someone mentioned that Encores had this stupid pickup design that had both coil magnets polarized in the same direction, I checked it with a magnet and discovered the North one indeed has this issue, while the South one does not. I flipped the magnet of one of the coils upside down. This haven't removed the hum and even restored the loss of low end issue, so I also reversed the phase of the coils connection (switched red and black wires). So now, the mess inside looks like this:

The North pickup's hum is gone. Both pickups have a full bodied sound. But a new issue occurs, one that was absent before!

Said issue is twofold:

- there is a constant silent hum that vanishes when the strings are touched; then both pickups work fine

- the pickups start to buzz really loud when the pole pieces are touched, but only if strings aren't touched at the same time (especially the South one has that problem, but it's probably due a bit more protruding pole pieces)
 

The pole pieces of the pickups are not grounded; they go through the coil's bobbin and touch the magnet on the underside.

The pickup slots are still poorly shielded; is this a shielding issue? I will shield it anyway, but I can order the copper tape only after Christmas. But do I have to do something else, too? Switch hot and ground wires on South pickup maybe (wouldn't this restore the comb filtering?)? Or maybe just flip the wires at the cable jack as now everything inside is reversed?

I'll just add that I can't afford to pointlessly tear the bass apart every 20 minutes as the pickguard is not stock and some screw holes are misaligned so each unscrewing ruins them further.

Thanks in advance!

Edited December 19, 2018 by Immo

[gary mac]

The buzzing pole pieces is a fairly common, annoying problem. Nail varnish carefully applied to the top surface of the pole pieces can help, as can using the same type of foil used for shielding the cavity, fixed to the bottom of the pick up, so that it covers the base of the pole pieces and then solder an earth cable from the foil to a grounding point.