Muting new users seems antisocial, but that’s not exactly what you are describing. It kinda seems like the root of the problem is that new users don’t understand the way Trust Levels work on DIscourse. It’s really only the jump from TL2 to TL3 that requires more than liking one post. 30 likes over 100 days (for TL2 => TL3) doesn’t seem all that noisy.
You can also adjust the notifications for like to be “Never” or “First time a post is liked”. (Admins can change the default for users as well.) “First time a post is like and daily” is the default, but I can image that getting noisy for people who have really popular posts.