Why is my Ford Mondeo's engine making odd noises?

I recently bought a used Ford Mondeo and I've noticed that the engine sometimes makes strange noises. It doesn't happen all the time but when it does, it's quite concerning. What could be causing this and how can I fix it?

It's possible that there could be an issue with the engine's belts. Check to see if they are worn out or loose and if so, replace them as soon as possible.

Another potential cause could be a problem with the spark plugs. Try replacing them and see if that solves the issue.

It could also be an issue with the fuel injectors. Get them checked by a mechanic and if needed, have them cleaned or replaced.