@TS: you probably found out by now but anyways: i think your avant is an old 81xx type and from the days almost everything was aired 4:3, resulting in the tube not 'burned' in equally.
The lighter sides is just the extra bit of screen, the difference between 16:9 and 4:3 (which is stretched to 14:9 or 15:9 by the avant).
Nothing to do about it....other than changing tubes.
@Bluecazzaf (although technically hijacking thread...): most likely the tube, a tech can find out easily...
Doesn't have to be total loss, if it's from 2003 it's RF ??
If ''cleaning'' the tube doesn't work (your tech may know this) for the 32" there is a cheap replacement still around (of course not from B&O), it takes some work though...but than it is as good as new :).