BTR3 battery level call quality issues

brusyev

I have purchased two new BTR3 units off Amazon and upgraded them to the latest 1.2 firmware. Both units are suffering from a call quality issue when the battery drops below 50%. The callers on the other end are hearing loud, wind-like noise and static making the call not possible. Strangely, the noise is heard when the call is placed from a completely silent environment. Once battery is charged above 50% the issue stops and calls are crystal clear. Is this a hardware issue or can this be fixed with a firmware update?
The issue is present when calls are placed from Samsung Galaxy Note 9 and S8 running Android Pie.

brusyev

Looking at the lack of response from FiiO I conclude that it would be better to move on to another brand/product...