Exhaust buzz

[The Platypus]

Hey guys,
I have a metallic buzz at about 2800 RPM all the way to 3400. It starts when I've been driving the car for a while and it gets louder on WOT. It is there when the clutch is engaged and the car is in gear. I looked on Miata.net's Garage section for the sound and it describes something similar and says it could be a crack in any of the heatshields, a rock stuck in between the heatshields, etc.
My question is : would it still be exhaust related if it only happens when in gear? Or is it possible that it's a transmission problem?

Thanks in advance.

[Johnnie]

Try revving the engine with the car stopped, in gear, clutch in. Hold it in the rev range where the buzz occurs. What do you hear? Try it again in neutral, clutch out. What you hear now? I would think if it's an exhaust buzz, you should be able to reproduce it somewhere in the rev range when the car's not moving, clutch in or clutch out.

EDIT-- Just checked out your build thread. Very nice.

[kung fu jesus]

I would recommend getting under the car and start putting a wrench on bolts under the car. No need to go retard-strong on them, just check for anything loose. Look for loose heatshields, too. Check the rear subframe for loose bolts on the bracing, see if the exhaust is touching the frame or differential.

[The Platypus]

@pass the peas
It only makes the noise in gear, clutch engaged, while moving. Not in neutral, not in gear with clutch disengaged.
And thanks for checking out my build.
@kfj
Alright. Will do. Thanks.

[kung fu jesus]

Where/what area is the sound coming from?

[fitftw]

Mine's doing the exact same thing, between 1600 and 2000rpm though, most noticeable on deceleration without pressing the brake pedal. Only with the clutch engaged. It's coming from right below me, in the cat area. I have a test pipe, not even a year old. Sounds kinda rattly sometimes. I changed the header-to-cat gasket the other day. Checked the heatshield above the cat but it's tight and not touching anything. No idea. Gonna change the rear cat gasket soon.

[The Platypus]

My sound is more noticeable on acceleration. I have the entire stock exhaust. It sounds like the sound is coming from the area below the shifter and closer towards the engine. I'm gonna take a guess and say it's the heatshield for the downpipe (I think there is one, right?)

[kung fu jesus]

Sounds like the heatshield for the cat.

[The Platypus]

Actually, upon a further inspection (I just popped my hood), I noticed that the heatshield for the headers is missing a bolt. This could probably be the problem, huh?

[ScarfaceThe91]

My car has a raspy/rattly kind of sound as well and does it most in certain rpm ranges but I believe in my case it's probably worn bearings in the transmission causing slack in the gears making the transmission noisy. The increase in the noise during certain rpm is probably due to harmonic vibration characteristics of the transmission but this is just my speculation based on what I've observed with my car. It might be worth looking into for your car though.