Q: Hear a knocking noise when car is in gear

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I have put around 1500 miles on my car since I bought it. When I bought it, I changed the oil (I put 8 quarts in). Well, after I changed the oil, I cranked the car and put it into gear, and it sounded like a hammer was beating on my fire wall. So, I put the car in park and the noise went away. It only knocks when the car is in gear, the A/C is on.

The car was at the mechanic for a few days and they are telling me the noise is normal. I went and listened to 5 other 5.0 Mustangs, and none of them made the same noise. I just got back from the Ford dealer, and they said it has something to do with the belts. But, I feel like it has nothing to do with belts because you can hear the knocking inside the car. Outside the car, you can also hear it and it seems to be getting louder.

I'm using Motorcraft 5W-20 synthetic blend in the car with a Wix oil filter. I can put my hands on the valve covers and feel it knocking. If this has something to do with the A/C drive belt, I feel like it shouldn't be this loud. I've also noticed a little tick noise right under the valve covers but it comes and goes. I have gone to two different dealers about the knock, and one dealer says that it's normal, and the other tells me to keep a eye on it. What could this be?

A: It is possible that the recirculation door ...

It is possible that the recirculation door on your vehicle defaults to a particular setting when the vehicle is in park, and the opposite setting when in gear. This could be due to the fact that more outside air is available to the climate control system when the vehicle is moving.

If the actuator that controls your recirculation door is not working properly, oftentimes you will hear this hammering type of sound. I would recommend taking your vehicle back and asking them to check the actuators on your air distribution system. It is very likely that the noise you are hearing is actually coming from under your dash.

Almost all engines will have a vibration that can be felt by touching the valve cover and can often be perceived as a problem when it is actually not. If an engine truly makes a noise, it would be checked with a mechanic's stethoscope to determine the exact location of the noise; a mobile mechanic can come to your home or business to inspect an engine noise for you.

Considering that you are using the exact oil that Ford recommends for this vehicle, I do not think that your noise is engine-related.

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