I raised an issue about this back with the iOS 11 betas and I'm bringing it up again here now because there's still not been a resolution come the 11.2 betas.
I am persistently seeing, across multiple iOS devices of several generations, issues with Bluetooth audio producing loud to very loud chirps and pops in the right channel of audio accompanied by a slight and quiet distortion.
The effect is most noticable when playing back relatively quiet audio and particularly with sounds that are alread "sharp" against a quiet backdrop. Quiet speech and plosives being the most notable.
I haven't confirmed this but I suspect there's some sort of cross channel issue attached as well as you can have a near silent right channel produce popping inline with audio on the left channel.
So far I've confirmed this issue with iPhone 6, 6s, 7, 7 Plus, 8 and X as well as iPad Air 1, 2 and Pro on iOS 11. Audio devices reproducing the issue include several models of Sennheiser, Sony and B&O headphones as well as car audio kits from Ford, BMW, Jaguar and Porsche. The issue occurs regardless of location, so I don't believe it's interference and I know for certain that it did not occur with my personal iPhone 7 and iPad Air 2 on iOS 10.
Is this widespread at all? I seem to be finding the occassional report online but I'd have expected it to be everywhere were it a universal issue.