The best way I can describe this sound is a hiss or like a plastic bag flapping in the wind. I jacked up my car and it seems to be coming from the y pipe or cats ( which are both stock) it is only noticeable when next to another car, wall, or a jersey wall. It happens when not moving and revving and while moving. When I get above 3500 rpms I cannot hear it any more. My cars rpms drop below idle and bog a little bit from time to time, hmm let me know if you think I should get aftermarket cats and y pipe because thats my plan but if their is a quick fix please let me know! thanks

 

No mention of miles?

Catalytic converter may fail internally, and make strange noises. Believe Nissan will give you a free catalytic converter regardless of miles.

Other than that you may be looking at new gaskets. Unfortunately you cannot see a "failed" gasket unless you take the exhaust apart. I assume gaskets are on your dime.

NOTE: If this is a exhaust manifold - motor gasket you have a big headache.

 

64,000 miles I sure hope its the cat

 

Sound coming from under the driver seat?

Hell, thats just the midget who lives under there who makes the seat go back and forth and pivot front and back when you press the buttons.... what?... you think they can afford to put real electric motors in there to do that? hell no. its all those umpa lumpa dudes from the Chocolate factory...now they work for Nissan !
Just throw a few crackers under there every now and then and she'll be right mate!

Gee

 

lmao thanks, its coming from under the car though. I'm going with Davidv's thoughts sorry