Why is my Vauxhall Insignia's engine making a strange knocking noise?

I recently purchased a used Vauxhall Insignia and I noticed that the engine sometimes makes a strange knocking noise. It doesn't happen all the time, but it's definitely noticeable. What could be causing this and how can I fix it?

The knocking noise could be a sign of an issue with your engine's bearings. I suggest bringing your car to a trusted mechanic to have it checked out.

It's possible that your engine is low on oil, which can cause knocking noises. Check your oil levels and top up if necessary.

The knocking noise could also be caused by a faulty ignition timing. I recommend having a professional take a look and adjust the timing if needed.

Another possible cause is worn spark plugs. Consider replacing them to see if the noise improves.