Pmruss I think signalProducer might be on the right track , is there a chance you can try a different digital to analog converter and see if the pops go away in idle mode, I use a designated headphone Jack on my older iPad and it’s for a number of reasons I don’t want to upgrade , this is one of them unreliable tack on devices that hang on the end of iPad really piss me off , I have had no issues with the old devices but I get very nervous when I use my new iPhone with a shitty tack on converter to give me a headphone out, I’ve bitched to Apple many times but they don’t care about real needs people they only want money from the people that don’t really use their devices for meaningful purposes , that’s life.
Good luck
Cheers Damir