Put the stethoscope on and test if it comes through the glass or the frame?
Of course you can do that. As far as I’m concerned, you can also run around the house with a dowsing rod. If your contract partner (builder, craftsman, manufacturer) recognizes that as proof of defects, all good. Or if that forms the basis for your decision on whether to leverage the not insignificant financial investment and replace the window glass throughout the whole house or even the entire window: even better.
But: I find it problematic to recommend such an approach to someone who is still under warranty.
Especially when
Walls in the house are very permeable to sound
a
window checked?
and
The energy saving ordinance is to blame
come up.
I’m out. Hopefully, the measures taken by the OP will resolve the described symptoms, and he will be able to register the costs somewhere.