I've had Cex not honour their 2 yr warranty on £225 AirPod pros. Order AL480365. Apple acknowledge the crackling is a manufacturing error and will fix. But CEX say it's earwax and told me simply to pick up my AirPods. I suspect it's because they can't go to Apple to resolve.
This is the difference between me continuing as a loyal Cex customer (I've bought various consoles and games previously and am a registered member) and never using again and use Apple / Amazon / eBay etc instead.
I will consider taking to trading standards if it can't be resolved.
Link where Apple confirm the problem can be easily found - type HT211157