I noticed a brief medium frequency rattle noise only at certain times. The dealer told me to wait until it gets worse so they can easily see what it is and fix it then.
They think it sounds like it’s coming from the transmission. I hear it coming from the engine compartment, more central sounding than anywhere else.
It occurs only after starting the engine, the first pass through the 18 - 25 mph range around the transition between 1st and 2nd gear or 2nd and 3rd.
After making this noise at this time, it will not make it again until I turn the engine off then on again.
The noise is independent of engine temperature, length of time the engine is off for, RPMs, and accelleration.
I have tested each of these potential causes and no matter what I am doing, at that speed, the noise happens, but only once per on/off cycle of the engine. (If I drive the car 7 times in one day, turning the car off between each time, I will hear the noise exactly 7 times)
I drive a '94 Mercury Sable 3.8L V6 with 58,000 miles and already replaced a blown head gasket. I do not want to also replace the transmission.
What do you think it could be?
Unless it is for warranty or recall service don’t go to a dealer. Take it to an everyday, reputable, local, independent mechanic and ask them to drive it. The first thing I would inspect would be the engine & transmission mounts.
If you do ever get good reason to suspect that it is something in the transmission itself, make it a shop that specializes in transmission work.
Thank you, I will get it checked out by an independent mechanic ASAP and see what their verdict is.
Chances are it is a component in the exhaust system, heat shield or something hopefully an annoyance rather than a big buck repair.