Power off noises - Laney VC15

I’ve had a Laney VC15 for about 10 years and recently it has developed a loud pop on power off. It’s about half a second after the switch has switched, so I don’t think it’s the switch caps. The electrolytics look ok, and the amp works well.
If I pull V1 the noise it there. If I pull V1 and V2 it stops.
Any clues where to look?
Thanks