The first question is, why do you need to sync audio for a music videoclip? Shouldn’t you just put the music track on it and completely disregard audio?
Second question, why did you import audio at 16bit if it was recorded at 24bit? As previously stated, it’s best to import at 24bit if recorded in 24bit.
This is my guess about what is happening: It’s a music video. They might have shot the video in slo motion (as is often the case in music video). So, the audio will always drift. Because audio will always be recorded in real time. In this case, don’t bother trying to sync all the audio files. If you need to use one bit of audio, just grab it and throw it in your cut, but you’re wasting your time trying to sync full audio rushes if the video was all shot in slo motion. Either that, or slow the audio down.
NB. I know you say the video was shot at 29.7FPS so it doesn’t look slow motion. But sometimes it appears that way in Premiere and needs to be manually interpreted at 60FPS or whatever to slow up properly. You should check with the cine what frame rate they shot at.