Since I updated my phone from D802-SEA-10F to Vodafone 20A i got same problem. When there's any audio playing over headphones I hear crackling and electronic noise in left earpiece. I've tried on few headphones - hifiman re262, akg k712 and stock lg. All headphones had same sound problems. I guess it's time to flash back the 4.2.2 and wait for SEA-20A...
You can try this. It makes the noise less annoying until next reboot.
http://xdaforums.com/showpost.php?p=51130511&postcount=82
How on earth has this issue got past testing? And then subsequently still got pushed out across the world (today in the UK in my case)?
For a supposedly audiophile phone, it now sounds like a cheapo 1980s personal stereo.