Stop iPhone from vibrating when recording a voice message in Signal or WhatsApp

Whenever I start a voice message recording in Signal or WhatsApp my iPhone SE vibrates. This vibration can be heard at the beginning of the voice message. The phone also vibrates at the end of the voice message, when I release the "microphone" button.

Since this happens in two messengers independently, I suspect that this is a system setting. I was not able to find an option to turn this off. The phone does not vibrate when I use the built-in "Voice Memos" app.

Neither the silent mode nor the do-not-disturb mode have an effect on the vibration.

How can I stop my iPhone SE from vibrating whenever I start and stop a voice recording in a messenger?

_{iOS 12.0 (16A366), iPhone SE (MP832DN/A)}

This is a system setting and can be fixed in settings.

Go to Settings -> Sound and turn off "Vibrate on Ring".