Brake, then grind then no brake?

[Ollie]

My car is still in for brakes but wanted to ask out of curiosity what was behind the following?

My brakes were down to 3mm when it was in the dealership a month or so ago, havent driven too far in it and last week I would brake and you heard the squeaking noise, then sometimes not always, you would hear a grinding noise, an electrical buzzing type sound and with the clutch and brakes pressed for 10 seconds or more the brakes would fail and the car would continue motion after the above noises with brake still pressed?

The brakes worked as normal, with some squeaking when just pressed with no clutch.
It's gone in for new brakes and it seems news brakes it is to be, was just curious if the above was normal for worn brakes or if something else has been overlooked?

[Ollie]

I forgot to report back, but my friend who is mechanic took the car for me and on route to his garage he slammed on the brakes twice and the grinding stopped.

The electric buzzing type sound I could hear I was told was the rear brake no closing properly or fully and the fluid was not getting in and this is what caused the electrical buzzing type noise (like in movie when a massive wire is exposed, that, zzzzzz type sound) I assume as it was trying to extract fluid, the noise came more from the passenger side.

Hope this is of some help if someone one day stumbles across it