Hi, I'm new to this site and am hoping to find some answers to a few questions that I have. I own a 2003 Expedition with a 4.6L V8. About a year ago I installed a K&N cold air intake and a Gibson catback exhaust system to try and get a little more power to pull our 27' travel trailer. All has been working good up until now. The operation is still good, but I have noticed a noise that I can only describe as a gurgle or a large cat purring. At first I thought it was the tranny, but I think I've narrowed it down to the intake system. The noise occurs when the A/C engages while at idle; the transmission is shifted from park to anyother gear and viseversa; or the throttle is just touched. The noise is more annoying than anything. Does anyone have any ideas. Any suggestions would be appreciated. Thanks in advance foryour help.