Lately, I've been hearing an intermittent squealing sound on my 2003 Silverado 1500. When it starts, if I increase my speed slightly it stops for awhile. I'm thinking either water pump or fan. How can I tell if it is either of them?

 

I vote for the belt as the noise source. When was last change? What's your mileage?

 

check both your belts for cracking, if they look ok remove them and spin the pulleys listening for noise

 

Belts. One way to check would be to spray the belts with a belt conditioner aerosol. If the noise goes away, it's a loose or hardened belt. I've heard of guys just rubbing a soap bar on the belt as it spins, but that sounds real risky if you get your arm caught in the belt or fan, so I cannot recommend that you do that.