Could this be the problem that I noticed earlier? If you look at the K&N closely the center is not very solid. I wonder if under vacuum the filter sucks in towards the center and allows dirty air to pass by the outsides. Pat Martin 864000csq 2 1/2 cat back, H&R-Boge,advanced and loving it. Drilled and stopping it. Koenig Cobra 16x7 with AVS Intermediates, K&N. 95 subaru legacy Bothell, Wa.