my amp making noise on power-up

[pula58]

My home built amp.
Single channel AB763 design using SIlverface bassman (50W) chassis. Solid state rectifier, standard Fender ab763 style reverb circuit, etc.

Lately, when I power it up I hear this:

http://www.seanet.com/~pauls/sunnyside_ ... n_cold.WAV

what the heck is that? The amp did not use to make this noise. (amp is on stand-by during the recording, the noise continues after taking the amp off stand-by)

When the amp is stone cold the noise is worse than when it starts up being already warm.

It seems like the noise is coming from the power tranny. When I reach into the amp (head) and push upwards on the bottom of the power tranny the noise stops (as long as I keep pressing on it)? Weird.

[Structo]

Sounds like transformer buzz.

It happens when the laminations vibrate.
Most transformers do it to some extent while others are clearly audible.

I would make sure the screws that hold the transformer together are tight but other than that, not sure what can be done about it.

[bandade]

have you tried pulling tubes? I would agree that it could be the transformer but I've heard a buzz like that from tubes.