Jura Z7 coffee problem

Hello, my name is Leon de Kock and new here.
Have been using Jura coffee machines since 2007. First a Z5 and now a Z7.
Always solved all problems myself. Now I am looking for a problem.
During the preparation of the coffee, there is a pressure build-up somewhere before the coffee is sent to the outlet on the left or right. To the right, coffee and espresso, is not that much of a problem. Coffee "explodes" in your cup, but remains delicious. But to the left, "special and cappuccino" is less fun. Your beautiful, white foam layer is immediately "ruined" by a coffee shower. I rather have that small breakthrough point in the milk. Which part can cause this" over-pressure"?