I get that noise on oober cold days, just started when winter finally arrived around mid January, at first I wasn't sure what it was, had my infamous concerned look on my face when I started her up one fine chilly day as mum and I were heading out to go shopping and moms like "what's that" lol...looking more concerned than me and I was like "I DON'T KNOW" lol. it sounded like metal grinding, better yet a disc kind of grinding, I thought the fan might have come loose or broke and was wacking something because from inside the car it sounded like it was in the dash but when I turned the fan off it was still there, then I thought it might be my clutch because when going along in first (not all the time) and letting out on the clutch it made the same noise just quieter, so alas I popped the hood cause it was driving me nuts and discovered after looking around that it was my heat shield...I knew it was eventually gonna start to rattle because the bolts holding it on were black back in the summer so it wouldn't be long before they went. Now I just need some new bolts but I may just leave it off.