Intermittent whining noise, mostly when braking

Hey all,

So I have a bit of a weird whining noise in my car, it seems to happen more when I am braking.
Initially I thought it could be the aux cable as it seemed to have started when I started using the aux (seems to be just coincidence as I unplugged the aux and its still there).
I then thought maybe due to the fact I had a rear brake bulb which was dead, although even after replacing the bulb it's still there.
I thought maybe the radio, but even with it off it makes no difference and after recording it and playing around a bit I think it may be related to the AC / fan ?

Hoping someone here can help point me in the right direction as to what it could be and how to make it stop! It's quite annoying, seems to happen more when I apply brakes but not limited to just braking. Sometimes while driving and sometimes while moving, with my foot off the accelerator but not applying brakes and sometimes while just stopped at a red light.

Here is a link to the video I took, I moved my phone around to try help pin point where the noise may be coming from and then it randomly stops.

https://youtu.be/I4pM_PU9Aik

The noise does sound a bit different in the video