Sound traveling though ducts

I have an in-law and I think I get a lot of noise traveling from the in-law to my house upstairs. I put in a ductless split for the inlaws downstairs and I'm wondering if taping the ducts closed would prevent noise from traveling upstairs or should I disconnect the ducts from the in-law? Thanks

source https://hvac-talk.com/vbb/threads/2228597-Sound-traveling-though-ducts?goto=newpost