My T-Mobile S21U when using HD calling emits some distortion from the earpierce speaker. That’s the speaker being used when the phone is against your ear on a phone call. It doesn’t make any difference what the volume level. One example is when you fall 611 for example but it happens with any HD call. My second handset exhibits the same issue. You need to be in a quiet room to hear it. It almost sounds as if the speaker is blown. It buzzes or crackles.