The red regulator, the high pressure one, is what is "whistling" etc. It converts tank pressure to 30 psi to go to the regular regulator. Here is a link to the OE Fairview high pressure regulator;
https://www.fairviewfittings.com/pro...ulators-37750/
If you look at the specs on this one it appears to be rated for 100psi. It does not state "max" but I did read that somewhere in my research on them (110 psi as I recall). I would not think that Keystone would install something like that either, but, nowhere did I see that the 630 is rated for 250 psi - anywhere. The Marshall units are (but they do have a 110psi option as I recall). Did I miss something? Possibly. Are those max numbers above 110psi available for the 630 anywhere I saw? No.
Just throwing it out there for consideration since I couldn't find anything saying my high pressure regulator was rated for anything near 200 psi...on the unit or in print.