Ok, did some research and found my problem solved…
Audio frame rates matter too!
Another audio trick I have learned the hard way is how to use audio frame rates. Yes, audio has a frame rate, just like video (who knew?) – and it’s important you get the right one when recording audio onto a separate device. Otherwise, your audio slowly starts to slip out of sync – a pain when you’re trying to edit!
A bit of research led me to this conclusion: set your camera to film at 24p and your audio to record in .wav form at 48khz. All good audio recorders should let you adjust these settings. This way, the frame rates match perfectly!
found at https://blog.vjmovement.com/?p=322