Get underneath the car and take a look. My brother just bought a 2013 Corolla and it had a shield rattle. There are various nuts/bolts that hold the shields in place, sometimes they just work their way loose and the rattle happens. Sometimes you just need to get a bigger washer to hold it in place more firmly. Can be a simple 5 min fix.

 

It's definitely loose. I had a better look at it today and the shield is not held up at all, hence all the noise. I'll have to try to get under the car this weekend, though it will get really cold (-20c).

 

Are you sure it's the heat shields? I had a rattle as well coming from under the car. Happened only on acceleration through 2000-3500rpm and had to be done while driving. Sitting in park and revving didn't make the noise. I crawled under and found 2 heat shields with issues. The front heat shield close to the engine was torn a little around a nut/washer and the long heat shield under the middle of the car had one nut/washer tear straight through it. I fixed both spots by using a bigger washer to hold up the heat shields but the problem was still there. Eventually narrowed it down to a catalytic converter problem and took it to the dealership for repair - luckily it was covered under the 8 year major emission warranty.

 

it happend to me when i drove into a puddle i just went under and readjust the heatsheild under the car and it went away

 

This happened to my 2007 Corolla. During the huge rain storm in Toronto this past summer, I drove into a huge amount of water and my car started to make a lot of noise. I found out it was the heatshield and that the screws holding it were rusty and just came right off in the water.

I don't think rust is an issue for you but the screws could have been weak.

 

So I got under the car last night, and the nut/washer that would hold it up are still there but the hole for it in the shield is now bigger than the washer, hence why it is now just resting on the cat. I can't get the nuts off either, just lack of room to work with and they are darn tight. I have enough threads though to put another nut on the bolt, so I might do that. I already have some larger washers that I can use, so I'll have to see if I can find nuts that will thread onto the existing bolt. Wonder if Toyota would sell just the nuts.