2007 Chevrolet Equinox

occasional clunking from transmission.What is the cause???

could be many things. Give us some more details about when you hear this clunking. In a specific gear? During accelerating or decelerating? all the time? What makes you suspect the transmission?

Give us some more details about the vehicle: what engine? how many miles? any recent work done on it?

It’s well known that there have been problems with Equinox’s transmissions.