HEAD SCRATCHER: Fender 62' AVRI Jazz Bass hums when Chrome ashtray covers are on.

[soma89]

Issue: Chrome “ashtray” pickup covers cause hum. Just hovering the covers over the pickups cause an increase in hum, getting louder the closer they get to the pickup. This happens, and is most obvious, when the pickups are both at equal volume and hum cancelling..
When covers are left off, bass is completely silent.

What I’ve tried so far:
-Alligator clips from bridge to bridge chrome cover
-Alligator clip from different grounds in the controls to covers
-Grounded copper shielding behind pickguard
-Continuity through all grounds in the circuit to bridge, control plate, output ground
-Purchased a new set of Fender Licensed chrome covers
-Demagnitized new and old covers with watch demagnetizer
-different pickups
-different locations.
- substituted in a completely different control plate




Any help is appreciated.