Half of serpentine belt brown

Leaving on a 550 mile trip in the morning so I thought I'd check my oil. Pop the hood and notice that half of my serpentine belt has turned brown. I assume this is probably rust coming off of something since I was able to wipe a spot of it off. The belt itself looks ok (no cracking or anything). It's a 2009 with ~73k miles. I'm sure it's the original belt (I've owned since 32k). Car runs fine and no unusual noises from the engine. It's been a few weeks since I had the hood up and I'm fairly confident the brown wasn't there. Any ideas what could be the cause and if it's something to worry about? Thanks.

Most modern belts don't crack, they just snap. Your belt is about 8 years old so consider replacing it along with the tensioner.
Belts don't rust, so not sure where the brown is from, probably dust from other stuff.
Free gauge to check your belt: http://www.gates.com/products/autom...t-wear-diagnosis/belt-wear-gauge/request-form
Nice YouTube to check out: https://www.youtube.com/watch?v=Clv2ZlS3hB0&t=0s

Check tensioner belt too...may be is not in axis.

The water pump pulley is painted black, over time the paint wears off where the belt runs and the bare metal starts to rust. Not really a big deal but it can cause a squeak noise after a while. You can replace the belt but you need to replace the pulley if you don't want the new belt to turn brown.

+ 1 @ hornsfun10609

I have the same problem.But I think is not necessary change the pump...problem of rust is only on cover ( external site ) of pulley.Pump of mine is ok ( 100000 km ).Cleaning a superficial rust on the cover with cloth is enough.