Weird noise from belt-tensioner or waterpump?

http://m.youtube.com/watch?v=BbtZl0DCbpc&feature=plcp

Can someone point me in the right direction? This sound appeared after I changed the thermostat, flushed and changed the coolant from BMW blue to red longlife. Can't really see the connection here. I did give the 32 mm fan nut a couple of firm knocks to change the fan and get better acess to work and change the hoses. Did not come loose so I decided not to deal with this for now.

Thought it was worth a try to upload the video here, hoping someone recognizes this noise?

Have been searching the forum and have a feeling it could be the belt tensioners.Could it be soaking it all when flushing? Or waterpump-bearing? Don't really know, but as I said...it appeared after this job was done! The noise does increase with rpm. Temp is steady 12 o'clock. And warms up much faster with the new thermostat:)

Thank you for any advice!

Thor-Egil 1995 M73

Flushing:

Thanks Reinhard!

Well, did stop the fan with a rolled up newspaper. The sound is still there. And my firm knocks was not very violent...next time I will buy the "special holding tool" (Ebay) The sound wasn't there before the job. So it looks like it is a connection here

Thor-Egil

OK...maybe it´s a good idea to change both pulleys then. Also going to change both belts and the remaining coolant hoses. The car is now 18 years old, is it recommended to change more...thinking about fan blade, waterpump itself, tensioners?