I have the exact same issue on my iPhone X during calls, an extremely annoying high pitched sound lasting for about one second at random intervals. There is no difference whether using the airpods (not the latest generation), using my bluetooth Bose headset, using the standard wired earbuds or just talking directly into the phone. Most of my friends have iPhones but it's certainly more frequent / intense when talking to some of them and I have a feeling that this only happening when both parties are on an iPhone but they have no similar disturbance when talking to me or others. This started happening about 6 months back and I have used this phone since its release. Wi-Fi calling is switched off on my phone.
As commented above, I have no issues listening to music (e.g. Spotify) or other media on the phone on the same devices - just during calls.