I have a 1993 Grand Marquis that has developed a strange intermittant sound that I can only describe as sounding like a fog horn. It seems to be more pronounced between 35-45 MPH when accelerating or de-accelerating. You can even feel a slight metallic vibration through the gas pedal when the sound occurs. Other than the sound, I have no driveability problems. I'm thinking it's in the trans, but when I am outside with the hood up it sounds more like it coming from the front of the car. Any ideas? I'm not reading any service codes. I did recently have the torque converter replaced under extended warranty but this sound developed some months later. One person thought a special lubricant wasn't added to the trans fluid to reduce the noise. Another thought it might be failure of the water pump or fuel pump but the car drives fine for now at least.