Vibrating noise while idling

My 1998 Toyota Corolla has been making a strange noise while it is stopped and the car is idling. It is hard to describe, but it sounds like something is vibrating or like something is lightly hitting an object while rotating. The car is an automatic, and the noise stops when I put the car in neutral. I don’t hear it all of the time, but it has been happening more often. I checked all of the fluid levels, and they are all okay. Could someone please help me to figure out what may be wrong and how I can fix it? Thanks!

Toyotas have a few heat shields and when in drive your rpms are lower than in neutral and they sometimes rattle.
Hope this helps

I agree that I loose heat shield is the likely source of the noise. This is probably best tracked down if you get the car up on the lift.

Is a heat shield something that needs to be replaced? Can it cause further problems?

As long as it is in place you can leave it as is.
The occasional rattling is not a problem.
But we haven’t proven conclusively that this is the
source of the noise you hear.

A loose heat shield can be fixed with a big band clamp that looks like a big hose clamp. A hardware store has them for driers and sewer pipes, you might have to connect two together.