Viewfinder hair only in one weird circumstance...

Hello everyone. I just received my first DSLR a few days ago, a T4i with 18-135 IS STM lens. It's amazing!

Today, I noticed a hair (or thin plastic shaving) in the viewfinder. The weird thing is, I don't actually see it when I put my eye to the viewfinder. When I put my eye to the viewfinder to take a pic, it's totally clean. When I use Live View for pics/movies, nothing shows up on the screen. When I review my pics taken with any aperture value, they are totally fine. The only time I see it is when I point the lens at a bright light and look at the viewfinder from a distance (ie: holding it like I would if I was using Live View). As my eye gets closer to the viewfinder, it goes away (too close to see it I guess, not in focus, blurs out).

In other words, this is a non-issue that I can live with, but I would like to know where that hair might be and what I could do to get rid of it (if I decide to do something about it). It's not on the outside of the viewfinder that's for sure. Adjusting the diopter doesn't change anything either.

Any input would be greatly appreciated.

Thanks in advance!