When ever I have seen a PS-1 chuffing with out running (moving) it has been a bad solder joint on diodes or something like that. I guess I don't ever remember a neutral chuff on PS-1. So I might suspect a bad chip unless the reset clears it.
I recently ran into a chip that started sounds immediately, never the 2 ding normal on start up. Could not enter any reset state. No type of reprogramming to the top board cleared it, so I had to replace the chip to resolve the issue. Never saw that before. So who knows. But neutral chuff put proper operation with no chuff is odd. Unless some sort of DC offset getting on to the board.
So for you try reset. If I had on bench I start swapping boards to see if I can isolate the issue. G