2003 Saturn Ion with low trans fluid

So I did my usual oil change and checked my transmission fluid which was low so topped it off after hearing a rattling sound from the engine. Looked all over to see if i could find it but nothing. What could it be??

You will have to let us know roughly where the noise is coming from.

Front of the engine, back of the engine, closer to the firewall, closer to the front of the car.

Without something more to go on…it could be any of 100 things.

Also please tell us how many miles are on your Ion, and what is the maintenance history.