Truth be told, I've never seen a Lambda driver fail. Break open, sure, but never just die on me. Even if the driver gets only sporadic "doses" of bias then they could play perfectly fine. The best way to test this would be to open them up (no need to remove the pads, just lift up the 4 corners to reveal the screws) but you could also try to bend the cable next to the earpiece and see if it makes a difference.