Some users have reported an issue with new iPads when connected to the Mac over USB. When capturing the iPad's screen and sound, an intermittent buzzing sound is heard from the iPads sound channel every 10 seconds or so.
We've confirmed this to be an Apple bug and unrelated to Ecamm Live. (The same sound can be heard when listening to an iPad screen recording made using QuickTime Player.)
The workaround for Ecamm Live users is to press the MUTE button in the Sound Levels window for the iPad's sound. Unfortunately, this precludes capturing sound from the iPad but can be a good workaround if you're not needing the iPad's sound.
Please file a report to Apple using the Apple Feedback Assistant and describe the problem in the best detail you can. Categorize it as an iOS bug and explain that it happens during iOS Screen Capture.