Microphone issues in messages only?

I cannot record a message in iMessage without it sounding all muffled and unclear. Every other app works perfect. Just in Messages. Apple said it could be software issue. I’ve spent the last two days following their instructions on the phone with them. Wasting hours and hours. It still doesn’t work. Anyone else have this problem. I have an iPhone 8.

Your comments, advice would be much appreciate. Thank you.