My wife has a 2004 GMC Envoy with about 60k miles on it. It makes this strange noise that sounds like rushing air in the back of the cabin when you get on the accelerator sometimes. The hatch is closed and all the windows are up. It almost sounds like a vent or some kind sucking or blowing air. It doesn't do it all the time nor does it seem to affect performance but it sure is annoying when it happens. I would like to figure out what this is and get it fixed.