I just did a quick test on the gamma settings; what I've posted has the gamma for the bump set at "same as render". If I change it to custom and set to 1, the effect is reduced quite a bit, but not eliminated. And yes, GC is set at 2.2. There are no displacement or specular maps. I tried plugging the bump map into displacement (just into dis, not into bump and dis) but the result was the same.