NB Weird Rattle at part throttle
 

New member here. I have searched, but haven't found anything on this. I have a 2002 NB that rattles in 3rd or 4th gear when cruising at part throttle in the 3-4K RPM range. Its not very loud, I can only hear it with the top and windows up. Basically if I cruise around in 4th gear and roll into the throttle between 3-4K RPM I get this rattle sound. The harder I roll into the throttle past say 20% in 4th, the louder the rattle. Light or no throttle, no rattle.

Any other time its fine, accelerating from lower gears or a stop is fine, cold start, warm start, no rattles. No CEL, car makes power like it should, runs smooth, everything seems fine driving wise. VVT actuator was replaced with a new unit from Mazda, but this sound was there prior to that, which make me think its A) Normal?? B) Something to do with the intake or C) A shield or something is loose that I haven't been able to find.

Any ideas or suggestions would be appreciated. Thanks!

Potential items making this noise:
-Aftermarket flywheel
-PPF Angle and resulting drive shaft angle
-Vibration damping thing on the diff coming loose and shaking around. I forgot what that thing is called.

I should mention the rattle is definitely coming from under the hood. Still on the original factory clutch and flywheel. I'll check the other two just to be sure.

My bet is a heatshield that rattles at the frequencies produced by the engine in that specific rpm range.

I have the same model year Miata as you, 5 speed, torsen LSD, and I am experiencing the exact same issue you describe. Only in 3rd or 4th gear, at the same throttle position/speed as you. I recently replaced my entire exhaust (Headers, midpipe, muffler) and replaced the OEM exhaust hangars with Poly Exhaust hangars, and had Competition Motor Mounts installed. I had my clutch and associated bearings replaced recently as well, however the issue remains. Also replaced the diff lube with some GL5 fluid and the transmission fluid with Motorcraft Trans Fluid. Does your car have a 5 or 6 speed trans, and is it Naturally Aspirated?

My current fix is to put the top down at all times

Mine is a LS, 5-speed with a Torsen. Mine is still 100% stock with 37K miles, I've only had it a few months. All I've done is baseline the car with some PM (TB, WP, Fluids, Etc). I noticed the noise a couple weeks after I got the car. Obviously its hard to say, but it sounds like the rattle sound comes from the passenger side of the engine bay. Have you replaced all those parts hoping to solve the rattle?

Regardless from where it seems to come, lift the car and check PPF alignment and diff snout damper clover thingy.

I used the rattle as an excuse to replace those parts, the clutch was due to my throw-out bearing being super noisy and likely about to seize. It had more than half of the ball bearings missing upon clutch replacement. I haven't checked my PPF alignment or the diff clamp thingy, I will look into checking that further and see if it changes anything. Also, yes, the noise seems to come from around the passenger side engine bay/trans tunnel. I will also be replacing the curly clutch line with a braided stainless steel line, as it could possibly be that line/one of the brackets rattling about/being loose.

Attached PPF Alignment Procedure

https://cimg4.ibsrv.net/gimg/www.mia...ae72857c70.jpg
https://cimg7.ibsrv.net/gimg/www.mia...ecd52158a3.jpg

https://cimg6.ibsrv.net/gimg/www.mia...2ebe311c9f.png
Flying Miatas IRL View