Help! Bass amp making airplane noise. Unresponsive otherwise

Hi. Always provide make and model, though a quick glimpse of the panel in your video tells me it looks like an Ashdown MAG 300.

I hear two sounds. One is the loud ak-ak-ak-ak sound, and behind it is a loud hum.

My first guess is you have lost filtration on one of the two main rails for the power amp. That would cause the loud hum, and it might at the same time make the power amp unstable, which would explain the pulsating sound.

There is a small cable that carries the preamp signal to the power amp, you might disconnect that to see if the noise involves the preamp or is only in the power amp.

So first verify the main V+ and V- supplies as clean and both up to about the same voltage (other than polarity). I have no idea what that voltage might be, maybe 35-50-80 volts, whatever. But V+ and V- ought to be close to the same.

If it does involve the preamp, then verify it has good 15v rails.

You can also connect the line out jack to some other amp for a listen. Does all that noise come out over there, or is that signal clean?