So I have a Huawei Y9 (2018) running Android 9 with EMUI 9.1. Whenever I'm on a call (I've only observed this with Messenger calls so far), all the audio from my notifications and media (if any) also get transmitted over the call and the other person complains about having to hear them. I don't know what's going on really. Any help?
Check for the secondary microphone on the phone (usually, it is near the back camera or top of the phone). This microphone is used for noise cancellation. Do not block it with your hand while talking on the phone.