Haven't seen this kind of fan failure before

Customer called me and said there was a "humming noise" coming from her computer.

When I got there the noise sounded more like coil wine to me. I figured it was either coming from the PSU or from the motherboard. It was neither.

I noticed the 80mm rear case panel ventilation fan was not turning. I checked the connection and it was not disconnected from the motherboard pin header. I spun the blades with my finger and the fan started turning on it's own but the whining noise became irregular, kind of staccato in nature. I disconnected the fan from the motherboard and the whine disappeared. So one of the induction coils had failed. I've seen lots of fan bearing failure but never this.

Fan is half dead I would replace it. Coil whine can come from GPU. I had "humming noise" from my new pc it was pc case had to screw it in harder meaning it can be anything. Also I would open panel turn it on and listen where is noise coming from. I am not electrician but broken fan can cause such sounds when they are unable to pull enough electricity, try with another fan or just disconnect that one to see will noise persist.

I wasn't really asking for advice, just offering my experience in case it might help someone else. Fan was replaced and all is well now.