Mazda 3 rattle under hood until warmed up

There is a rattle on passenger side under the hood that will go away after the car warms up. This only just started happening when it got really cold out. Don’t see any heat shields in the vicinity.

I fixed my own problem. I figured out that the belt tensioner was bad and once I replaced this the sound went away. Sounds like this is a common problem with this year mazda.