16khz treble spike in bass guitar pot.

[CoolName]

Hi. Anyone care to offer a theory as to what's going on here with my bass? Treble control on bass all the way off in one picture. Treble all the way on in the other pic. There's a 16khz spike when the treble is on. The more treble you add on the bass the bigger the spike gets.

Fender P-Bass about 5 years old.

Thanks