2 broken fan belts in 8 months?! '03 4.6is
 

So I was driving home tonight, it was 6 degrees outside in NYC, and a few blocks from the garage I heard some rattling from the engine. It almost sounded like plastic pieces flying around the engine so I got scared that it might be my timing chain guides that broke because of the bitter cold. I have 128k miles so you never know. I stopped the engine to make sure I wouldn't destroy it if that was the case. I popped the hood and realized that it was just the fan belt that broke and pieces of rubber got caught in the fan. I just replaced both belts 6 months ago after the fan belt broke last spring. AC was working perfectly (haven't used it in months though) and I even replaced both tensioners! What could cause two fan belts to break 8 months apart?

Are you using OE belts? I would check all of your pulleys and see if they are in good condition.

Misalignment!!!

Yes, always OEM parts.

What could be misaligned?

+1 - Something isn't lined up correctly most likely.

Let's see some pictures of the belts. Do they look excessively worn on one edge? Torn up on the grooved inside or on the smooth back? I know it will be hard to tell after getting sent through the fan...
Also one of the pulleys could be sticking or has physical damage that is rapidly wearing the belts. Or, any fluids leaking onto the belts?
I guess last question, are you driving 100k miles/year? The belts are only good for maybe 70-80k max.

I only drive about 8k miles a year since I live in the city. It's probably been about 5k miles since it was changed.

I can try and get some pics but I don't think they will help much. The belt looks like shreds of rubber.

No leaks, all my hoses are brand new. I'm thinking that something is sticking, but the AC was off and has been for months. What else is looped in to the AC belt?

This is the AC belt that broke by the way, not the serpentine belt. Sorry, title of the thread is unclear.

Tensioner could be misaligned, you mentioned replacing both tensioners. And using your socket wrench you can move the AC tensioner with moderate force correct? If for some reason the tensioner isn't moving, it could be making the belt too tight which will overheat it and wear it very fast.

Only other thing would be the AC compressor is not lined up correctly. Has that been replaced, or any other work that would have for some reason required the compressor get R&I'd?

If the crank pulley were out of alignment the other belt would have broken also and your engine could possibly be rough running...

Look at all three pulleys on the AC belt carefully and look for any nicks/cracks/debris stuck in the grooves.

OEM parts meaning from the dealer? Should be Continentals if bought 3rd party.

P.S.
You should use the AC once a month for a whole drive cycle to keep all the seals from drying out and to keep the compressor lubricated. Plus it helps defog your windows quicker in the winter.