dito. ALC850.
First, when i wanted to try out the sound i recognized those scrytchy alert sounds - so i looked around and tried different kexts.
Then i found out that - even with the original kexts - sound works fine (itunes, alerts from third party apps, even from mail). Only the original alert sounds make that noisy sound - if they are played by the system.

All kexts which i tried didnt solve the problem.