Trouble with projection tv's is the intensity of the beam used to produce a sufficiently good projection image, increases chance of image burn. (Although coolant is used in front of the lens.)
If you think it is image burn, write to Sony Customer Service a.s.a.p. and ask them to consider helping with any repair cost or even press them to repair it under warranty, as It's just 3 months out. If you don't ask you won't get and nothing to lose.
(Although, if you look at the manual it probably does, or should, warn you against prologed use in any mode other than full screen image, or against displaying channels showing logos and video console games at high contrast settings.)
However, if you ask firmly but politely, expressing your disappointment, manufactures can be suprisingly helpful, especially if they are aware of any issues with their products. But do act quickly.
Regarding the fault,..
If there is a distinct image of the 4:3 border then at least one if not all of the three cathode ray projection tubes may be permanently affected by central phosphor burn, not the front screen itself. Some manufactures are apparantly introducing service modes to produce scrolling white bars to even out the image for similar problems on Plasma displays, not heard of it on projection sets.
If there isn't a distinct image of the 4:3 border but just seems brighter in the area of the 4:3 bars, maybe could be lens flare, especially if you only notice it on bright images against dark backgrounds. Some say viewing in low ambient light can help.
Also, if the focus or convergence is poor (from one or more of the tubes), the further from the centre the worst any fringe 'glow' on whites will be, which may cause the sides to appear brighter.
Good luck.
Cobweb, January 2005