The "garbage" pixels that appears on screen usually are a symthom that the RSX solders are broken :/
Is soldered by a method named
https://en.wikipedia.org/wiki/Ball_grid_array
Under RSX there are some hundreds of small solder balls... and most probably you have one (or more) broken
To repair this is needed a reballing... that is made by desoldering RSX and cleaning all the old balls and replacing them by new balls... and soldering it back to the motherboard with an expensive machine
The other way is a reflow... by this method the balls are not replaced but melted with hot air, but this is not a permanent serious fix... usually the problem appears again after some tenths of hours of use of the console