Warwick Thumb Bass Pre-amp noise

[goingdownslow]

Haven't used my '90 Thumb Bass for a while and when trying it today, when I inserted the jack plug there was a static type electrical noise, like something being turned on, it lasts two to three seconds and then all is fine. It will do it again after removing and re-inserting the plug. It never used to do this and my other Thumb Bass, a '91, doesn't do it. A new battery doesn't help.

[paul_5]

Is it not just the capacitors/opamp filling up after being empty?