Used Bongo 4HH – bridge pickup hum

I’ve noticed a bit of a hum, static noise, coming from the bridge pickup only. I can sort of dial it out with the EQ, but that defeats the purpose of having an EQ.

Anyway, I noticed some metal shavings on the pickup poles (I assume from some ill-advised person using steel wool to clean the frets without masking off the rest of the guitar…). I vacuumed and blew them out as best as I could, without taking the pickups out and attempting to remove the plastic covers.

The electronics in the control cavity appear to be OK, and the pots are not scratchy at all when operating them.

Any other suggestions to try?