Why is my Ford S-Max's engine making a loud knocking sound?

I recently purchased a used Ford S-Max and have noticed that the engine makes a loud knocking sound. It only happens intermittently and seems to be more noticeable when accelerating. Can anyone provide insight on what might be causing this and if it is something I should be concerned about?

It's hard to say for sure without hearing the sound for myself, but it could possibly be an issue with the fuel injectors or spark plugs. I would recommend getting it checked out by a mechanic to be sure.

I had a similar issue with my Ford S-Max and it turned out to be a faulty belt tensioner. I would suggest having that checked as well.

It could also be a problem with the engine bearings. If that's the case, it's important to get it fixed as soon as possible before it causes further damage to the engine.