noisy fan belt?

Recently my 78 Midget has developed an interesting squeal.  This only occurs at 
4000+ RPM.  I can only assume it is the fan belt.  Why it would sqeal then and 
not other times I am not sure.  Belt dressing helps but only for a short while.

Questions:
Is it conceivable that this is something OTHER than the fan belt?
At first glance it appears to be a good size project.  Tell me I am wrong, 
please.

 I can record and post the sound if needed.

Thanks as always,
Steve