Left Airpod Much Quieter than Right

My (3rd Gen) Airpods don't function properly.

The left one is MUCH quieter than the right - if I have full volume up for the left one, it's still barely audible, however, the right one is deafening at the same time.

I have done a factory reset/forget this device via bluetooth, etc etc.

I have cleaned them.

Using the 'balance' slider in audio settings on any of my other devices (MacBook, iPhone) does nothing to fix this, so please don't put that as a suggestion.

I am completely at a loss.

Is there anything else I can do before writing off yet another Apple device?

Thanks.