Originally Posted by BalanBro

I have the ARK with Berks. Thiss hiss/whistle is normal, the metal rattling is NOT. Sounds like a clearance issue with the install.

Also, I had a rattling right after my install too. It turned out that plug for the extra O2 bung on the Berk HFC was not torqued down properly from the factory and was rattling loose. Tightened it up and the metallic rattling was gone. Don't know if yours even has that O2 bung, but it's worth a look.