I made a stupid mistake and now got a strange problem on hand to deal with...

The other day I replaced the radiator, during the process I started the car and droveforward for about 3 feet. But I did not bother to reconnect the tranmission fluid pipe and I heard a grinding sound and immediately turned the car off. Already a lot of fluid leaked out.

I put everything together and added transmission fludi. But ever since then, whenever the car started to move, I can always hear this grinding sound from under the car... Once the car started moving, everything is fine though.

Can someone give me some suggestion what I might have damaged?

Thanks in advance.