Recipient's getting echo on voice calls

[Hazer]

Sp I just recently upgraded to a new S21 from a Razer Phone 2 and been liking it so far.

Apart from on all voice calls the other person hears themselves all the time. I even tried on a second mobile and it's really bad.

After googling it seems its quite common, is there any fix for it? It can't be a carrier issue since its the same sim cars from previous phone and it happens on WhatsApp calls aswell

[Huds]

Old thread but I still have echo issues on S21 Ultra,  but only when using an earpiece or Bluetooth headset,  never when using phone only. Tried the *#0283# test (many thanks to @AndrewL above for that suggestion). and this enabled me to solve one issue,  using the wired earpiece.  Turns out the usbC to 3.5mm adaptor was causing the echo,  and trying a different adapter results in no echo.  So at least I don't have to hold the phone to my ear for hours any more. 

Now to solve the echo problem with Bluetooth headsets & earbuds (I've tried a few). I'll share any useful findings. 

[JJbilbo]

I changed my network Mode from 3g to 4g LTE/5G and this seems to work.

[Huds]

Thanks for the idea. Mine is at 4g/5g, which is one reason I bought this phone. Therefore I won't even try throttling any features.

[Jeff_C]

I had the same problem.

Turning off WiFi Calling fixed it.