i used to have a xoxowhatever "stage 3" bov from ebay and it wouldnt open even with 10psi. so i just cut a few coils off and it was one of the nicest bov ive heard and loud. But if you say its non adjustable, then maybe go to like home depot or a hardware store and see if you can maybe find a similar spring that is lot softer and replace it.
good luck

 

Well i ended up cutting off a total of 4-5 coils off the spring and now it sounds/works perfect! $33 shipped to my door, you cant get a cheap/shittier then that!