Yeah, there are several threads about that in the subreddit [0]. I did get the ringing in my ears when I first started. The solutions normally given are a) You are straining yourself. "Listen to your body" when to stop holding your breath (No issues there for me) and b) Breath in through your nose, out through your mouth.
Breathing in through my nose completely removed the ringing noise for me.
[0]: https://old.reddit.com/r/BecomingTheIceman/