981s weird hissing sound on braking

[longi]

I have returned from a 1k mile trip at which end I drove whole day in heavy rain. After a week the car have suddenly started doing weird hissing noise inside the cabin, when i put the roof down i dont hear any noise from brakes outside.
The brakes also feel weird and not as reactive and strong as before.
Can anyone pls help determine what that might be? ytube below with the sound, i also tested the brake pumping with engine off and pedal dropped couple cm.

https://youtu.be/e1z6ecvOYAA

[SV_WDC]

Have you checked the brake fluid?