Small humming from engine area when car starts up
 

Hi guys, I can hear a small humming noise from my engine area on my 2005 s60 when ever I start the car in the morning or when cold. After getting warm the noise seem to go away. Tried listening for where exactly the noise is coming from but cant seem to pin point the area.

Any ideas what could generate a small but annoying hum??

Thanks

A video of it would help a lot, thanks.

Do you have the heat/ac on when you do this? Mine does it but only when I have the heater or the AC compressor on.