Audio latency issues can create lag or distortion in some devices. Unfortunately, in some cases this is due to specific apps that may be hindering performance or clashing with existing services, and in some cases it may relate to hardware.
First, shut down all other apps when using Tully App and see if that helps.
If that does not resolve the issue, you can test the latency of your device by using the mobile test provided here: Latency Test
If your test results show a latency greater than 10 ms, please contact firstname.lastname@example.org directly and we will try and help you in other ways, but we will need to know more about your specific device and setup.