I have just been playing around with the patented BCIEM setup of a behringer P2 and KZ ks10s and gone from the worst to the best sound ever, I had loads of crackle and couldn't trace it, tried various leads and muting every channel, tried the other P2s (I have 4 now) all the same, yep they were on stereo not mono!
With that sorted I was happy again but decided just 'to try' the other size ear buds that come with the KZs, the small were far too small and they fell out, the large are much better and the BASS is there in spades now, cracking!
I am blasting some Paramore through them🤘