How close is the downpipe to the headers? Mine vibrated on that to and I felt it at my feet when I shifted from 1st,2nd,and 3rd, then after it was fine
Only time i hear it is when i go uphill or accelerate when the road is leveled. The headers maybe 4 or 5 inches longer than the oem ones. I've literally looked into everything and I have no clue what it could be. I lifted the car and moved around under it.