yup yup yup.

 

The fan is definitely spinning immediately at startup. It might be that the fan clutch squeaks at low rpm, but its definitely turning

 

If you want to find out what is squeaking on your truck you are just going to have to start taking things apart. I am betting fan clutch also, but the belt needs to come off & you need check the resistance of your fan clutch & get a feel on your pulleys for a bad bearing.

 

it's not a matter of if it's turning or not, it's a matter of is it turning at the same rpm as the motor. You can clearly hear the fan speed up after that noise goes away.

 

Try this, for giggles. If the fan clutch is not engaged, it can be stopped with a rolled up newspaper. Try and hold the fan at startup, carefully and in a way that will not hurt you and see if you have the chirp with the blade not spinning. I think this will tell you a lot about what is going on, or at least rule out the clutch as part of the problem. It WILL engage shortly after startup, so be careful.