So I installed my headers two weeks ago, and going back over everything in my head, everything should be on right. First, when i dropped the car off of jacks, it unweighted the frame and loosened one of the cats, resulting in a loud puttering sound, like some shitty old caddy. Well, i fixed that real quick, and tightened every bolt, but there is still an underlying puttering noise ONLY when i am in gear. I took my car into the shop twice and had them tighten every exhaust bolt from the engine back, yet the sound persists. I had a mechanic ride with me, and he said he didnt know what it was, but hes ninety percent sure its not exhaust. Is this just the normal sound, or is it somehting that could be losing horsepower?