Apple has posted the following announcement on their web site. Seems that they may have had a faulty batch.
Apple has determined that a small percentage of AirPods Pro may experience sound issues. Affected units were manufactured before October 2020.
An affected AirPods Pro may exhibit one or more of the following behaviors:
- Crackling or static sounds that increase in loud environments, with exercise or while talking on the phone
- Active Noise Cancellation not working as expected, such as a loss of bass sound, or an increase in background sounds, such as street or airplane noise
Apple or an Apple Authorized Service Provider will service the affected AirPods Pro (left, right or both), free of charge.
Replacement, naturally, can be facilitated through an Apple Store, service provider, or by contacting Apple directly.