Card in the spokes
 

I'm driving a 1995 s10 blazer with 135000 miles on it. It has just begun to make what I can only describe as a very loud "card in the spokes" type noise. This notice is constant at low speeds and goes away on the highway. While it's there it is constant in volume and speed. It is there while the vehicle is in park or reverse as well as drive. It also putters out after the motor is off. I'm assuming it's the trans but if anyone has any thoughts I would love to hear them. I added trans fluid with no change.