gears P12

I have the following Question :

Now and then when I swith from gear 4 to 5 around 90km/hr, I hear a small noise from the gear shift. When i pull it a little bit back the noise almost always stops.

I thougt I had to do with the backwards leaver, but i turns out that this is not the cause.

The noise dissapears when the speed is at about 100km/hr. So the noise only appears when the speed is between 90 and 100km/hr and when I accelerate

I drive a wagon 1.9dci from 2003