Funny Flue Noise - Help?

[DoubleClutch]

We have an old VC Intrepid II cat stove on a tall (maybe 36') SS stack, and sometimes when I open and then close the stove after loading it, the flue starts making this funny sound like sheet metal rattling. I will try to attach a file of the sound. Can anyone tell me what this sound might be, and what it means? Thanks,
DC
Edit: I see I can't attach a sound file...oh, well.

 

[begreen]

Sounds like it might be small flakes of creosote burning off.

 

[JimWalshin845]

OMG.. you have flue critters... terrible little buggers... sweeps hate them.. very contageous! ;-P