1999 Dodge Caravan Strange noise on shift up or down

Hand me down van, runs well, no engine lights etc on but the van (I'm assuming it's the trans) makes a strange sound after shifting up or down. I can only describe it as the sound of a thimble on a washboard sort of a creak. It seems to be shifting fine, though being this is my first vehicle I cannot be sure, no obvious thumps, jerks etc.
I have heard many other old vans give the same creak as a pedestrian.
I did have a leaking/rotted trans pan replaced a couple of months ago, but the creak has been there all along and continues.
Any ideas?

Thanks for your time.