I along with many others, have been facing a low frequency noise leak when ANC is fully on and music is playing. https://discussions.apple.com/thread/256148548?sortBy=rank

Without playing any music the ANC is stellar, but this bug means the buds are basically unusable as they require reseating in the ear, or toggling to transparency and back to ANC, after a few seconds of listening (if in an environment which has any sort of constant low freq noise)