Hi,
This mainly sounds like an interconnect issue. Check the integrity of your cables and that the connectors are properly seated, there are numerous issues with HDMI leads as I discovered.
OK,
Can you turn everything off, take the switcher out of the set up and connect the ATV2 (I assume) direct to the TV? Do you still get crackling when listening without the switcher?
Shop for your Apple, Mac, iPhone and other computer products on Amazon.
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.