Mine does too! I always thought it was just the way I was sitting being different, but no it definitely does this. Happens slowly so that I have to adjust it once every couple days, but it definitely happens. It's the auto-dimming mirror right?
Once upon a time I had:
2012 SGM SEL Sedan Job 1 BD 6/2011
FSWERKS Cool-Flo w/ ITG Filter | FSWERKS Stealth Exhaust | 17x7.5 Axis Sport XMX Graphite wheels | Eibach Sportlines on Ti Handling Pkg bits