Originally posted by twitch It's not lens and I doubt it's the card (by all means rule it out by trying a different card).
I strongly suspect you have a faulty sensor
I am afraid I agree.
To me, this also looks most of all like a faulty sensor. Maybe some of you remember the issues around 2003-05 with Sony CCD sensors (used by a major group of camera manufacturers then) where images gradually degraded in a few cameras now and then.
As I recall it, the issue with these sensors was the gradual de-bonding of a moulded epoxy layer within the sensor, and it sometimes manifested itself in the same manner as we see here...........