Just as the topic says, my PSU makes a what I would describe as a buzzing sound when it is on, the sound is very feint and you can't really hear it unless you put your head close to the PSU, I have confirmed it is coming from the PSU but is this normal?

The buzzing also comes from the PSU when it is off, since the PSU tends to stay on for a few minutes after the PC shuts down to keep the fans running for a bit longer.

I never noticed this before so I'm not sure if this is normal or what, my PC is about 3 months old now.

The PSU I am using is a Be Quiet Dark power pro 750W.

Any inputs would be appreciated, thank you.