We’ve all had this problem.
It’s cold solder joints on the analog board.
Open up the computer, take off the white shield (those black plastic push rivets come apart, and can be reused), and start soldering.
This is one of the simpler fixes, as there’s not a whole lot of taking apart, but if ya don’t have a 9” T-15 screwdriver to open the case, it’s not easy at all......