You need to get it fixed. Exhaust leaks in front of the O2 sensors can jack up the tune. I had a header leak so i bought the MM max grip kit so i could have a tubular k and access to the bolts. Without a tubular K the bolts are damn near impossible to get to without dropping the K. You can use a piece of ~1/2" tube to your ear, and then move it around until you hear the air whooshing. Many times it will be easier to hear under a bit of load.

 

i installed jba long tubes with a non cated h pipe and had wat i thought was an exhaust leak i went nuts titening all bolts and clamps i couldnt fix the problem i stoped at a couple of performance shops in my area and let them hear the noise they all said the same thing "most if not all long tube headers have loud resonation" and this is wat your hearing after about 2 weeks of driving the car, the sound subsided quite a bit i guess they need to break in.