2000 Nissan PathFinder: hissing under acceleration

I have a 2000 Nissan PathFinder that exhibits an audible, but not especially loud, hissing noise under medium acceleration. It seems to be coming from the rear-right side of the vehicle, and is especially noticeable when I’m driving by some kind of solid object on the side of the road that reflects sound waves, like a telephone pole, guardrail, etc.

I can’t localize the noise when the car is stopped and idling, even if I get out and walk around.

I haven’t noticed any odor of exhaust in the car, nor any symptoms of carbon monoxide poisoning. Still - could this be anything but an exhaust leak?

Sounds more like a vacuum leak. Take a short length of hose, about 2 feet or so will work. Stick one end in your ear and place the other end at all vacuum line connections. Even at an idle, this should make the hiss loud enough to hear. Exhaust leaks tend to make more of a farting sound than a hissing sound.

Before you check anything, is your vehicle supercharged? That could be the noise (although superchargers tend to make a high-pitched whine more than a hiss.)