Nasal sound

[Herb]

I have a problem that's cropped up in the past few months that seems to be getting a bit worse now.I'm getting what sounds almost like a 'nasal' sound when I'm driving, and it goes up and down in pitch as the engine revs up or down.Originally I thought it was the exaust as one passenger thought I had modified it. Since I had minor damage to the cat after hitting a rubber wheel chock a couple of summers ago I thought perhaps now something's given way.However I did notice recently when I turned off the vent fans the noise went away so it's probably not engine/exaust related.I thought if it's the HVAC then the noise should occur even when the engine isn't on, but it doesn't.I'm a bit frustrated at this and hope someone out there has an idea what's going on, or for that matter what I'm talking about.

[Mavrik]

if you have a developing exhaust leak... it could be small enough it requires some load on the engine to be heard. It could change pitch to with the engine rev. My guess only though,