Hi, for about 6 months now I’ve been hearing a rattling noise in my engine. Seems to only happen when my car is idle (like at a stop light), or in park. I know basically nothing about cars, but I can say that it started to happen after breaking really hard once, but I don’t know if that’s the cause. I took a video of the sound, but am unable to post it on here as I am a new user. Maybe someone could help me out! Thanks much 
A mechanic will be better able to tell especially if it can be duplicated. I had a rattling sound that turned out to be the timing chain slapping against the cover. It’s mechanic had no idea but 2nd one knew.
It could be an exhaust heat shield rattling.
My vote is for a heat shield rattle which is not uncommon at all with any make of car.
You might try wrapping the tailpipe with a towel and then whacking it with your fist while listening for any rattling noise.
Since the sound happens at idle, ask your shop to use a length of old garden hose as a sort of stethoscope to narrow down the noise location. Good ideas above, ask your shop to check those first. Ask them to check for broken exhaust hangers too, while checking the heat shield. This sort of problem could also indicate internal engine damage, esp if oil and filter changes deferred beyond Honda’s maintenance intervals, if engine oil level ever got very low, or if cooling system has ever severely overheated. Anything like that?
Posting audio/vdo files here usually isn’t very helpful, sound quality not good enough to be diagnostic. That’s best done by a shop tech listening to the car in person
Don’t you think that a professional mechanic’s shop is likely to have an automotive stethoscope?
Shut off the car, get out and give the tailpipe a good kick or whack it with a rubber mallet. If you get the rattle you hear, it’s exhaust related. Never mind something similar already suggested.
Don’t know if all auto shops have a commercial version or not. I don’t recall ever seeing a mechanic use one myself, but I don’t hang around auto shops. I’ve seen a pro mechanic use a long screwdriver for that purpose one time.
Can’t help it. Like asking your doctor if he didn’t have a piece of garden hose to use instead, telling him that’s what I use. Me thinks that might be why customers can’t go into the shop area anymore.
Well there is that, and of course lawyers. 