While meticulously cleaning my aluminum frame the other day, I noticed a sizable "dent" behind the derailleur. There weren't any scratches to indicate that it had suffered any maltreatment and it was in a very inaccessible place. Admittedly, I panicked at first!

I am quite surprised it had gone unnoticed for a full 2 years. In the weird lighting, it looked as if the indentation might be uneven but upon closer inspection, it turns out it is quite a uniform, flat surface.

Is this sort of frame modification common practice? Does it compromise the integrity of the frame?