I don't support ANY fanmade Types like Cosmic/Light etc., but out of curiosity I wanna speculate what their Type matchups would be.

For Sound Type it would be SE on Water because sound waves travel much faster in water. Grass would resist it, because vegetation is good at breaking up sound/plants don't have ears/you talk to plants to help them grow. Flying Types would resist Sound Type because they control the air element so sound waves would have less effect. I know that Ice Type is glass-like so should shatter but SNOW is particularly famous for absorbing sounds, so they could make Ice resist it or take Sound neutrally.

Unfortunately I think Sound would need to be SE on Rock, it's not really an optional match-up. Because that's easily one of the most common ways of displaying sound-based superpowers—they can produce sound waves so intense they shatter rock. Kinda like how Fighting is SE on Rock because being able to crush rocks is a common display of cartoonishly strong muscle power.