I just got a 1997 4 door Grand Prix SE with the 3800 engine. When you get the speed up to about 30 mph, you get a noise that I can only compare to a coffee percolator. It is the same noise and cadence whether you are accelerating, cruising or decelerating. It is not a regular rhythm type sound like I would expect from a tire or rear end type problem. When you increase speed it does not get any louder either. It kind of sounds like wind buffeting noise. I looked briefly under and wiggled the muffler and what I believe is the charcoal canister in the driver side rear of vehicle but everything seemed tight. Any thoughts on this?