Buzzing sound while turning volume switch.

I have a BC21 and recently when I turn the volume switch, what could be the possible caused and is there anything I can do?
either the amp too old or your place too humid (like seashore or near hill)

need to get tech man to clean the blemishes (if any)
Or there's a loose connection. The BC21 is wired point-to-point and some of the components are supported by the wiring. I had a similar problem with a BC 21 which deteriorated into more noise. Cured with one dab of soldering iron. Open it up and look for something loose, probably connected to volume control.
You should contact Angela at
Tell her I send you if you want.
have a knowledgable tech spray the volume pot for you with an oil-free cleaning solvent (& then work the control end-to-end several times before the spray dries - tech should know to do this). If the symptoms continue then move on.
*IF* the buzzing isn't present when you're not touching the unit, *AND* it's fairly low in level when you are, I wouldn't worry about it too much, as it's probably just one of those little grounding anomolies having as much to do with the AC line and the combined other gear in the system as the component itself.
Bob and Zaikesman give good advice to my mind. Sometimes merely working the control end to end several times can help and make the buzz go away. If that does not help, unplug the unit from the mains, wait a little if it is a tubed unit, open it up and do the spraying yourself. (If the unit is new, which I doubt from what you say, you may however void its warranty)
Thanks guys for the advise. I'll open up the unit to do some spraying as what Detlof recommended. Anyway the unit was almost 3 years old.