I watched that video. One thing to note is that he has the sensitivity on "Manual" rather than "Auto". This will often cause less stable tones on the E-Trac. Nevertheless, what you hear there are fairly typical tones for the E-Trac.
You can watch this video of mine for another example. The video rambles on too long, but you can hear what a silver quarter at 6"-7" deep sounds like at the 10:13 mark.
https://www.youtube.com/watch?v=R0ugdrWtMnE&t=613s
I have the headphones plugged in but I think you can still hear the tones.