Is a slightly louder mains hum a sign that a valve or valves might need replacing?

[noisepolluter]

It's more of a high pitched buzz - it actually replaces the initial mains hum that you get for a few seconds when powering up.

I tried swapping back the stock GT valves that I took out when I bought the amp and subjectively I didn't notice a difference - I haven't yet A/B'ed against the other amp.

Thanks all for your suggestions so far - if a proper A/B comparison shows no difference I'll book it in with the local chap. Probably a good idea to do that every couple of years anyway.

[noisepolluter]

Update: after a power valve swap and proper A/B comparison, both amps' noise levels are now normal. I've tried plugging them in various places to rule out interference.

*shrugs*

I did tweak the lead dress slightly in the (previously) noisier amp when swapping the valves. That may have had an effect, otherwise I have no idea. I'm fairly sure I kept the valves in the same order through the changes. Oh well, no further action at the moment anyway, which suits me.

Thanks all for the tips.