My 2005 with 207,XXX recently started making and weird humming-like noise in the engine bay. When I start the car there is the normal engine note but there is also this humming noise that goes with it (almost sounds like the A/C fan but that is not on). The noise continues most of the time when I am driving and sometimes briefly gets louder when I stop. Any idea what this is? I couldn't find a similar problem on the interwbs.

 

What's an AC fan?
If this noise is more like a coffee grinder buzz, than your chain tensioners failed.