Had a strange experience today. Kickdown to get on the motorway and suddenly a loud sound, almost like those cards you clipped to your bicycle with clothes pins when you were a kid. It was clearly RPM related. But when we slowed down to stop it gradually faded away and disappeared, never to return. I suspected something fanbelt (the fans of modern cars aren't beltdriven, I know, but I always think of them as fanbelts) related, but can't see anything that looks wrong.

Any ideas?

Hi Knut Are,

My first thought on reading your question was - never heard of this one before - but after a moments reflection on your playing card in the spokes analogy I remembered an occasion when a large pebble or stone got lodged in one of my tyres which produced a broadly similar sound. May also be worthwhile checking to see if a nail or other sharp bit of metal has been driven into the tyre and is now below its road contact surface?

Let us know what you find - who knows could be my turn next.

I still call them fan belts. I think it's worth checking all round it for damage. I had a car where the belt split inwards from the edge a few mm and left a thin strip of belt flapping about which made a racket. 

It seems to me that the space blanket heat shield right next to the leftmost belt pulley was touching the pulley, or, as Laz suggested, a piece of the belt was flapping against it. Note to self: replace belt at next service.

While probing around under the hood, I also noticed that the coolant level is low. Thorough inspection didn't reveal any leaks. Argh! And grrr. Note to self: It's an old car, consider replacing all hoses at nest service.