New to the forum,

Bought my first mini, got it home and heard a strange whining / whirring noise from the engine.

Anyone got any ideas what this could be?

Please see below video, thanks.

 

Hello, first thing to do is remove the accessory drive belt. This is the belt that runs the alternator and water pump. It sounds like the bearings in your alternator are going bad. By removing the belt and starting the engine you can start to eliminate water pump and alternator that may be causing the noise. Be careful and don't run the engine very long with the belt removed. Just long enough to see if your noise goes away

 

X2 ^

In addition to that, you can audibly probe with a mechanic's stethoscope or long thin screwdriver. Just don't stick it in the wrong place...