low-high pitch humming in the front of my engine

How should I go about diagnosing a low-high pitch noise coming from the front of my engine?

The next day after a good 6 hour road trip from Salmon, Idaho I discovered a higher (some might consider lower) pitched humming coming from the front of my engine. It's not the common squealing like what normally might be the drive belt but I can hear that it has the same cadence to the idle of my engine. Accelerating increases the noise while coasting keeps it at a constant.

Manual 2007 Taco White access cab

 

Apparently you are not so lucky

 

I accept the irony.

It was the alternator btw. Around lunch today it was having troubles turning over so it was pretty quick figure out after that.