That makes it a Lycoming 0360, I think. I take it you're talking about the electrical pump making the noise, not the engine-driven diaphragm pump. We need some more information. What 'large' sound did you hear? Was it a rattle or grinding noise? Do you get any indication on the fuel pressure gauge when you switch the pump on?
Once the engine has started, it doesn't need the electrical pump to keep the engine running, which makes me suspect the fuel supply (the noise could be the sound of the pump suddenly running off load).