D-string volume too low! What's up???

Okay, so I've got a weird problem with my Tune Bass Maniac 4-string...

I just re-strung it with TI flats, and it sounds better than ever before. It's a P/J bass, with an active preamp.

On the bridge pup (jazz), the D-string is *markedly* lower in volume than all the other strings. I don't have adjustable pole pieces, but even if I did, the difference is so large I don't think that would be the proper solution.

Oddly, the same problem is not present on the neck P pickup.

I'm baffled. Any ideas, bass geniuses???

 

Any hints on what to check for? I'm pretty adept at setup, and this bass plays killer. I know it's not a string height issue, as I've got the strings adjusted perfectly.

As for the P/J, I find it a versatile combination. Why on earth would you recommend a P-only over a P/J? I mean, if I just want a P, I can roll up to the neck pup. I've lost nothing, and I've gained a growly bridge pickup for more bite if I want it.

 

Okay, it's not a setup problem. By tapping on the pickup with a hex wrench and listening through my amp, I've located a "dead spot" right under the D-string where the metal wrench doesn't make any noise at all... so it seems to me that this is a pickup problem. Anyone heard of something like this before? Could this thread get moved to "pickups" where it belongs (I believe)?