Aleph 5 - buzzing sound when hot?

My guess is it needs rebiasing. That is a common problem with well-used class A zero-feedback designs.

Send a note to Pass and ask (check the Pass website for contact info). I don't think the Aleph series has adjustable biasing. Is this a mechanical buzz or some thing you hear through the speakers?

I never had this happen with my Aleph 3. I did have mechanical buzz from other components (Wadia 830 and JJ 828), and in both cases, it was the power transformer. I agree with Ghostrider. Whatever it is, will probably require factory servicing if you can't / don't want to live with it as is. If you are a good do-it-yourselfer, you may be able to replace it, but you would still need to contact the factory to buy the part. I have not heard anything bad about Pass Labs service department, and vaguely remember hearing good things.