At random I cranked the car and this really loud grinding noise came from under the hood and I immediately shut it off and tried it again. And well, it did it again. Had the oil changed and that didn't work. It sounds like metal is being thrown around under the hood and lasts about 30 seconds before it stops. It usually happens on a cold start and has been at it for 3 days. Please help. I'm not very car savvy but Im very good with google and youtube. Just need to be pointed in the right direction

 

Could be anything from an accessory bearing like the alternator, (minor job) to an engine bearing. (big job) It is VERY hard to diagnose engine noises over the internet. Take it to a garage and have someone listen to it.