Has anyone experienced a distinct knocking sound after the engine is shut down? I have a 2017 Mustang GT. The installation done at Ken Grody Ford in Carlsbad, CA. The knocking started about one week ago. I took vehicle back to KG to see what the knocking was. I was told the knocking was happening due to the vehicle now having an open air box!!!!! Additionally, I was told the FP Stage 2 was an aftermarket part not made for made for my vehicle!. Any and all comments appreciated.. Thanks