What's this noise?
 

I've just had my head gasket replaced and on the way home this noise started. There is a constant whine and a rattling sound at certain RPM (particularly around 2000).
http://youtu.be/2I5k2mBHyj4

Any ideas?

From reading around, I'm thinking over-tensioned timing belt or a shot water pump but would like to hear from someone with a bit more knowledge.

Thanks

I'd make sure the accessory belts aren't too tight first, since they're sitting right there.

Thanks. I used a stethoscope to listen to the ancillaries but couldn't hear anything odd except coming from inside the head.

In the end, it turned out to be a bad idler bearing.