Rattling/knocking engine sound
Hi Everyone, I'm Kinda new here so please excuse any errors.
I've had my 318i for almost a year now. I travelled out of the country for the Christmas holidays and returned after three weeks to my car. after driving for a while I noticed some rattling noise in the engine. it was quite loud and sounded like someone was slamming a hammer on a piece of iron at the pace of 5 hits a second. I've never experienced this before. So i checked the dashboard computer, oil and coolant levels and all seems fine. This doesn't affect my driving at all though but it worried me so much, I had to stop driving it. At a point when i left the engine to idle a bit, the noise became so loud, I had to switch off the engine for fear of breaking something. I even thought I perceived a different smell from the engine...or maybe I was just being paranoid, I don't know.
But this morning, i decided to switch it on again. Surely, the rattle was still there. I revved up to 3000rpm and let it settle down again. This only seemed to aggreviate it more as the rattle became louder. Then I drove out and went down the street, put it on neutral (its automatic) and floored my throttle till it read 7000rpm. I heard a pop/cough sound from the engine, and let go of the throttle.
The knocking sound had stopped completely!
So I guess my question is, should I be worried about this? is it a common occurrence or did just happen because I hadn't driven it for 3 weeks? What causes this and how can i prevent it in the future?
Has anyone experienced a knocked engine on a 3 series before and could this be a sign my engine is about to knock?