I am not quite sure of how to add background to the weapon icons other than having the current blurry pulsing [that's not really a background, but at least a change of focus]. Since all other elements [music equalizer, font] don't have a strict background shape, I think it doesn't look nice to simply put a white square in the background. I know your pictures only refer to the size, but am just saying that for the future.

The idea of the resizeable HUD sounds very nice, though.