Strange exhaust sound

[Israelpr]

My 2002 QX4 has 143000 miles. It was never real quiet but lately it has a strange sound that appears to be the exhaust system. It's not real loud, but it sounds as if it had "an air leak" if that makes any sense. I checked under the hood and underneath and I can hear the sound more when I am under the SUV as oppose to under the hood. Does anyone have an idea as to what the problem can be? Thanks.

[zach7685]

Check the flex pipe and the flange. The way I found out was to start the car and put your hand on the tail pipe. As the pressure builds you should hear the leak. Also Sea foam works quite well XD