AirPods suddenly quieter

So - after the last firmware upgrade my AirPods are quiet on all devices, even on max volume and when compared to EarPods volume (so not a volume restriction issue). Bluetooth and online fixes dot not work. Weird thing is ... when I open sound preferences on my MacBook and select the "input" tab, the AirPods reconnect and sound like they used to. Leave that tab (e.g. to the output) and after 10 seconds they reconnect and back to low volume. Anyone else got the same problem? Thanks