I have just installed a POD filter to my Subaru legacy TX type s, 2.0 L. Whilst performance has definitely increased, there is a low whistle that has appeared that seems to be coming from a vacuum hose attached to the air intake. I am assuming that the factory filter setup must have somehow muffled that sound, as it wasn't there originally. Does anyone know how I might be able to fix this?? If I cant I will probably go back to the factory setup, its very irritating.