Horrific crackeling at power down...!?!

Ugh. A new problem. When I power down my amplifier (Bryston 4b-st) I get a truly horrifying crackeling / static sound through one or both speakers for a couple of seconds. I mean, this is a really scary sound, under the circumstances. I unplugged everything, recheched my ground, and it behaved. Once. Now it's back. Having exhausted my pathetically meager bag of tricks for dealing with electrical woes, what do I do? I'm half afraid to turn it back on again and, on the occasions when I do, I am even more afraid to turn it off (which I do rarely, in any event). Has happened three times, currently off. Help? Many, many thanks.
A temporary work around, of course, is to disconnect your speakers before you power down if you are concerned about damaging them. I am not familiar with how your amp normally deals with changing bias as the voltage bleeds down. Perhaps someone else is, or contact the manufacturer.
Assuming you don't have another item of equipment ahead of the amp signal input switching off just ahead of the amp you may have something "leaking" to ground which you should get checked asap. Agree with Sndsel, contact Bryston as they will be more than helpful. Good luck, Richard at www.vantageaudio.com
Contact Dennis at the Bryston U.S. service facility. While i no longer have a Bryston amp, he / they are phenomenal to deal with. If you send them an email via their website, they will typically respond quite quickly with the necessary info and phone numbers. Good luck and hope it's nothing serious. Even if it is, you won't be out much money at all due to Bryston's warranty. Sean PS.... When is the last time that you checked the humidity level in your house ? This sounds like a longshot / freak thing, but you might be surprised what a lack of moisture in the air can cause.
Interesting thought re lack of moisture--it IS exceptionally dry in there over the winter...maybe not such a long shot after all. In the meantime, I'l will drop Bryston a line. Many thanks to all.
Mezmo, I've had this specific problem just as you described with the left channel of my Bryston 3bst. I wonder whether there may be a design flaw in the Bryston gear? I contacted Bryston, and they advised me that I likely had a 'mute' problem (whatever that is - sorry, I'm no engineer) and that I could return it to get it fixed. However, last month, I had a party at the house so I moved my system to the living room to entertain. Upon returning the system to my bedroom I find that I no longer have any trouble at all - perhaps it was just a lose connection or something. Anyway, I suggest you return it to Bryston - their service is great, and of course free. Good luck.