About a week ago I got my ride back from the mechanic. They did some basic maintenance like an oil change and a larger job to swap out my old throw out bearing. When I was driving the car home I noticed a weird rattling/knocking coming from where the engine and the tranny meet. I don’t know what it could be and I’d like to hope my engine with only 200,000km doesn’t have rod knock. The oil is topped up on the car and the noise does not go away when I press in the clutch. Does anyone know a solution?

Sounds like an exhaust leak to me. They had the exhaust system off to replace the TO bearing, might have destroyed the gasket at either end of the cats.