Rattle on old start - Mini Cooper Coupe SD

[garnbag]

Hi, apologies if this sounds like a newbie type question, first post and also first Mini I’ve owned. I purchased a Mini Cooper Coupe SD (2012) around 13 months ago from a Mini dealership, still has TLC pack and had its MOT and brake fluid change in September, re: it’s history it’s only ever been back to the same dealership. It’s done 33,000 miles, I’ve personally done 6,000 in the last year. On starting the car yesterday from cold (hadn’t been used in 5 days) we heard a distinctive rattle sound coming from what appeared to be the engine, lasted no more than 30 seconds or so, I actually got out of the car and thought it was coming from an area somewhere behind the drivers side wheel, I bent down to have a better listen and the noise stopped. I started the car from cold again today and it didn’t rattle, I did however open up the bonnet and putting my ear close to running engine there is a faint alternate rattle coming from the back of the engine (Ie different to the everyday engine noise), trouble is the engine is very noisy as it is. I’m by no means no expert, done my own research (wish I hadn’t) and the only thing I keep coming back to is timing chain issues, but people commonly say “my car sounds like a diesel”, which ours is, so I’m a tad confused. I can’t find very much info about our model car suffering from those problems specifically. I’ve checked the oil level and it seems fine, the car also otherwise drives fine, but I haven’t driven it very far for these reasons. Admittedly I don’t really know what I’m looking at under the bonnet. Any thoughts on what the problem could be?