I've had this annoying rattle for a few months now, and I've eliminated every probably cause. I dampened my foglights that I mounted on the bumper, I checked the engine for lose brackets, I even removed my bug guard.

This rattle occurs when the engine is at high RPM (2500 or above), but only when the car is coasting (no clutch, no throttle).

The noise seems to be coming from the fire wall near the top of it. I removed the windshield cowling and checked for stones that might of been trapped inside (there were none).

I just tried replicating the noise while stationary in neutral, and I was successful. Because the noise happens when the vehicle isn't stationary I can rule out suspension. I shot a video of the noise from the interior (occurs at 7 and 11 sec mark).

I also did a recording in the engine bay, but it's harder to hear the noise. In the video it doesn't sound too bad, but it's worse in person (especially on the highway).

My main questions are, does this sound like something that could come from the engine directly?

Why does this noise only occur once I let off the throttle?

I would lean that way given it's clearly reacting with throttle input, but as for what it could be or why it's doing that is beyond me. I've never heard anything like that personally. If it can be replicated in neutral and maintained for a period of time then I'd have someone step on the gas while you poke around the engine bay, or maybe try holding the cable throttle open. Regardless I don't think it's any accessories in the front end like the cowl and whatnot

Should I be worried? I've had to drive with it like this quite a bit, and I'll have to do a lot more driving soon.

I've had some debate about it being from the interior. I'll get to hear it from the engine bay tomorrow, hopefully it settles it.

I did adjust the valves and when that happened I had to remove the exhaust camshaft. I followed the instructions in the service manual to the letter when I reassembled it, and used torque wrenches for everything. I can remember this noise being there before I did that too.

To me anyway, it sounds like a loose bolt. I had a similar noise like that coming from my transmission area of my 4Runner, turned out to be a loose exhaust flange bolt from my cat! Tightened it back down and no more noise. Take a peek around there? Maybe a rotted exhaust hanger/heat shield or a loose skid plate?

I am having a particularly difficult time looking at the spot behind the engine on the drivers side. There are a lot of loose wires and hoses sitting around and I can't tell if they are suppose to be tightened down or not. A lot of the plastic brackets have snapped or no longer sit snugly.

I took off the lower dash and bezel around the gauge cluster in the hope that the problem would reveal itself or at least become more apparent, but it didn't.

I noticed that if I hit my fist on the intake I could get it to rattle, I traced it to the throttle spring whose concentric coils could vibrate against themselves. I thought I had it, it even explained why throttle position was important, but I adjusted it with no luck.

Next I'm removing the skid plate and looking up. If I can't find it I'll take it to a mechanic and have them look.

Found the rattle, it was a plastic bracket on the firewall that no longer fit snugly in its hole. Pretty simple, but hidden in plain sight