Wavy Rear Window?

[zythen]

I noticed when I bought my truck that my rear window was kinda hard to see out of, upon further inspection the glass is wavy. You can physically feel the ripples. It's not consistent at all so I figure its a defect, I believe the rear cab seam was welded at one point, is it possible that they heat warped the glass?

More importantly do you think it's a hazard of any sort? It feels solid but I'm not sure how badly the structural integrity may have been affected. I just don't want it blowing up into the back of my head some day.

Thanks.