What do you mean by the bottom? What part of the set is affected and how was it determined that these parts were not the problem? Under what conditions does the problem exist? Menus, inputs, signal types?
I have not seen symptoms like you describe and your image is not very helpful. Any suggestions would be nothing more than a guess without having the set to evaluate. Even then, it might be guessing. You still have not given any information about whether menus are affected, nor what kinds of inputs you are using? Analog, digital, HD, NTSC, component, composite, tuner, etc.