knocking sound

[Calgary Rob]

There is a knocking sound coming from the left side of the car. It is fairly quiet, and sounds like someone is tapping the side of the car. It usually last for about ten seconds then goes away. Also happens at any speed.

 

[Orion]

There is a knocking sound coming from the left side of the car. It is fairly quiet, and sounds like someone is tapping the side of the car. It usually last for about ten seconds then goes away. Also happens at any speed.

What kind of car?