I bought my Cornford Roudhouse 30 a month or so ago.
It's been fine, but today when I was going through songs to get ready for band practice, towards the end of my little practice a massive buzz was coming from the amp, like regular tone and volume, just a really loud buzz.
I fonzied it in "I did not spend £480 on something that's going to piss me off" anger and it cut the volume for a second (don't hit your amp >_> but the buzzing stopped and the volume returned and all that.

But yeah, is there anything to worry about?
Is this a sign of "The guy who sold you the amp knew it was ****ed so he loaded it off onto you"?
And are there any solutions?

(it wasn't any of my other gear btw)
Have you considered turning down the bass on your eq? this happened to my Dad's amp on the A string, drove me crazy.

Was the amp plugged into a different power outlet than usual? It almost sounds like a grounding issue.