This looks like an issue with the TF300's. I checked a different forum, and appears other TF300 owners are having the same issue with the high pitch sound. I hope Asus can fix this issue with a firmware update.
Sent from my ASUS Transformer Pad TF300T using Tapatalk
The thing hasn't been fixed yet. Bad thing for Asus.
In think I'll stick to may Galaxy S2 for the job. Besides, I find it uncomfortable video recording with a tablet.
Sent from my ASUS Transformer Pad TF300T using Android Central Forums