Series 2 rectoverb loud pop on standby?? Help

[torquelive]

I have a series 2 rectoverb. When i put the amp on standby i get a loud pop crackle kind of sound. Doesn't seem to affect anything as far as tone but i have never heard this before in any recto i've had except for this one. only happens when i flip it on stand by. When i flip the standby switch up to "play mode" its fine. Any ideas??? Concerned i'm heading for trouble.