When recording a layer the sound gets very loud very quickly. What's going on?
If you are not using headphones, and instead either using the built-in speakers on your device, or you've got your device plugged into an external speaker system, you may experience something similar to feedback.
The sound you intentionally record will come into the microphone and record onto your loop. The next time around the now recorded loop sound will play through your external speakers and instantly be recorded again by the microphone mixed into the exact same loop. This effectively doubles the volume of the loop on every pass.
Possible solutions include turning down the volume on your speakers, making sure the speakers point away from the microphone, or using headphones.