Coolant sign Appeared, fixed the leak, but engine is making a rattling noise. on 2001 Audi A4 Quattro

One of the hoses got detached from the coolant reservoir( I think it got detached because of built up pressure). I attached it back with the clamp and screw it had, but now the engine is making a rattling sound. I was thinking it could be an air bubble, but I'm not an expert. Does anyone have advice that I could use before I decide to take it to a specialist?