My 2001 Ford E250 Econoline squeaks just for a moment when I start vehicle. Could it be the crank angle sensor? Hard to determine exactly where sound is coming from. Please advise. Thank you.

Got to be a fan belt. Try removing the belt, free spinning the pullys and check for rough bearings or noise. Make sure the belt is clear and try starting the motor for a moment. If it dosen't make the noise, you know it's got to be the belt or a pully.

Agree with jershu3. Best to replace the serpentine belt, tensioner pulley, and idler pulleys every 80,000 miles.