It certainly sounds like a poor cartridge/wire connection.
Try polishing the cartridge pins with a piece of Mr. Clean Magic Eraser (the white side, not the blue.) You could also try a Q-tip dampened with contact cleaner or alchohol, but take great care not to get any solvents near the suspension of the cartridge.
To make sure your cartridge clips make good contact, slip a wooden toothpick inside each one and squeeze GENTLY with a needlenose or forceps. (The toothpick prevents squeezing the clip too much and flattening it out.)
Try polishing the cartridge pins with a piece of Mr. Clean Magic Eraser (the white side, not the blue.) You could also try a Q-tip dampened with contact cleaner or alchohol, but take great care not to get any solvents near the suspension of the cartridge.
To make sure your cartridge clips make good contact, slip a wooden toothpick inside each one and squeeze GENTLY with a needlenose or forceps. (The toothpick prevents squeezing the clip too much and flattening it out.)