Rattles when idle

Hello everyone, just a quickie,

My car is making a deep rattling noise when idle, especially when its been running for a while and is fully warmed up. It seems to get louder the longer Ive been driving in it. I can hear that the rattle is coming from the offside, almost sounds like metal on metal just behind the the wheel arch. Any ideas?

Also, feels like the car is generally not as responsive as it has been, it has been re-mapped with Revo software about 10000 miles ago. Finally the oil light came on today, flashing yellow, don't know if thats connected (or just sensor getting faulty) there is plenty of oil in.

Thanks for reading hope to hear from someone soon.

Dave