Possible rear end 'howl'

When travelling at highway speeds, around 70 mph or higher I get a noise that I'm thinking is from the rearend but may actually be a leak in the exhaust. It sounds like a low growling noise, the car is relatively silent up until about 70 then therd is a definite murmur coming from somewhere. There is no vibration back through the stick that would suggest a drive line problem and the shifts are crisp and smooth. I have no visible leaks in the rear end...I'm hoping exhaust so I have an excuse to go with a 3" system from the turbo back!! Any thoughts as to what this could be?

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1987 Turbocoupe, no mods yet
1999 Contour SVT

If you want to get a better idea of what the noise is, take the back seat out--the bottom cushion just pops out if you press towards the back of the car on either side and lift up; the back is held on with the two Torx bolts that secure the seatbelts. The sound that those cushions insulates from the back of the car is absolutely amazing. Try it and you'll see. Don't be too startled when your PRC stuff kicks in, it's kind of loud. [Image: smile.gif]

BTW, my 93 Cougar had an audible rear end whine over 45 mph with the back seat out, but I could never hear it with the seat in. That was probably 25k miles ago and it's never gotten any louder.