I took my iPhone X and my KSE 1500 to Shure UK today. By the time I had got there the spare KSE1500 had gone out but we did try a new cable and the popping stopped. Sure then tried with the old cable and they could hear it immediately, swapping it back and it stopped. I left with the new cable and a happy heart.
Sadly this evening, the popping is back, only with the iPhone X and never using my Hugo 2. Both Share and Drew think that the KSE1500 is not compatible with the iPhone X, or at least it isn't until Apple fix the issue. Are there any X users out there having no problems? I cannot really understand why the Hugo 2 does not hear the pop but the KSE1500 does.
I have a X (and a 7), I'll try tomorrow to see if I can reproduce the problem, but I don't know if it have the cable that comes with the KSE1500.