So a couple months ago my Barista Express got the not-uncommon buzzing and low pressure that's usually due to a bad solenoid valve. I ordered a new valve which was backordered for 2-3 months and just did the replacement, but I still get the same buzzing and low pressure during a shot and often times a constant buzzing after the shot that only goes away when the machine is turned off. Pretty much exactly the same as before the valve swap.

Video of the loud buzzing: http://www.youtube.com/watch?v=az-t3LNyFYM

This is after I ran a tank of descaler, a cleaning cycle of Cafiza, and two more tanks of water through with constant loud buzzing throughout all of that. I then tried another backflush/cleaning cycle with Cafiza and the rubber blank but water wouldn't come out at all during the cleaning cycle due to constant buzzing. I ran another 2 tanks of water through with constant buzzing and I'm all out of ideas.

So anyone know the next steps after replacing the solenoid and still getting buzzing? Appreciate any help as I'm sure I'm going to have to DIY this. I don't live in a city with any shops that services espresso machines that I know of.

Any chance it's still under warranty?

Most shops that claim to service espresso machines don't want to work on Breville gear.

That sounded like it kept turning the pump on and off and cycling the solenoid rapidly. Maybe loose connections somewhere? I doubt it but i would worth looking at.

I'm leaning towards a bad control board, but that's just a WAG at best.

I think you're onto something with the bad control board. I unplugged the solenoids and tested the water output from the pump. The pump works fine when the cables are not connected to the solenoids.

But when the solenoids are connected, buzzing occurs when the pump reaches high pressure and water stops coming out of the pump. Also I get a slightly different sounding buzzing if I stop a shot or at the end of a shot, maybe a bad board is causing both of the solenoids to misbehave and the slightly different buzzing sounds are because the two sound different.

I already did many descales and even cleaned the inline filter screen with a Waterpik but that didn't help. A bad board is probably the only thing left.

Have you checked the pumps output?
Disconnect the hose from the pump and see if any water is coming out when activated.