Okay have kind of a cool noise coming from the car but it's more then likly not a good thing.

Here it is, when I am driving from time to time I hear a noise coming from under the car that sound like a blow off valve on a turbo. (Which would be cool if I had a turbo) My thought is that exaust is building up in the pipe due to a blockage from some thing and releasing it's self some where. Dose anyone have any thoughts on this matter. I am thinking that it may be the cat in going out.

Any Ideas on this would help.

Thanks
Chris