What you might try is to find a deserted stretch of highway, carefully shift to neutral below around 35 mph, turn the engine off, then listen for the sound. If it sounds exactly the same, you can rule out engine-related stuff. Look for tire wear or a broken belt. Normally a broken belt will be felt as one corner of the car hopping up and down a little and there will be a shimmy in the steering wheel. However, ... There is a way for a broken belt to only be heard and not felt. If the break is small and occurred over a long period of time, as one spot in the tread grows a hump it will wear off from driving. That makes the tread appear perfectly true as you watch the tire rotate. What you have to look for is a hump in the grooves between the tread. A lot of mechanics forget to look for that because it isn't so common. Many people aren't even aware of that. What you would be hearing is the tread squirming sideways each time that weak spot in the carcass contacts the road. If you do not hear it while coasting with the engine off, you will probably still hear it while the car is standing still with the engine running. If so, suspect a worn serpentine belt. A quick way to identify that is to see if the sound changes when you dribble a little water on it.
Monday, March 14th, 2011 AT 6:28 PM