Aleph 5 - buzzing sound when hot?

Thanks for your responses. Its definitely a mechanical noise and not from the speakers. Someone told me that all US amps with serious power supplies buzz because of the 50Hz mains electricity, as they don't use toroidal transformers or other power supplies, preferring classic core transformers with iron plates because they are sonically better and offer fast response and resolution. I don't know if this is plausible, but I will get in touch with Pass Labs as suggested. Thanks again. I love this forum thing - never used it before!

Apparently the Aleph does use a torroidal transformer, so this is unlikely to be the cause, although the bit about the 50Hz electricity can be true. Anyway I have contacted Pass Labs. When I get a response, I will post the answer here.

Latest news from Pass labs is that the Aleph 5 deos use a toroid - made in the UK (so shouldn't be an electric current frequency problem). They suggest that with age and temperature, it could be a meltdown of the Sorbathane pad underneath the transformer. Apparently if pad
melts, it's a bit messy, but not a safety or performance issue. Guess I need to take a look inside!