Looking for some help identifying this noise
 

Car is a 2006 Base, manual transmission. Engine is a 6 month old Mazda reman installed under warranty by a dealership with approximately 3700 miles. Car also has a BHR coil kit.

I was accelerating up an on-ramp when the car lost power and had a CEL (not flashing). After pulling off since something was clearly wrong, I noticed the engine was making an unusual racket.

Towed the car home, and pulled the code - P0302 (rear rotor misfire). Started the car up without issue, and idle seems normal. Cleared code did not reappear (misfire was temporary?) When accelerating to about 4k in neutral, the engine makes a loud racket. Due to the noise, its difficult to tell exactly where in the engine bay it comes from. Operating the clutch has no significant effect. Both the VDI and SSV move with little effort, but manually operating them has no effect on the noise.

Based on searching, I don't think this is the SSV shutter issue. All the descriptions and videos I've found do not seem to line up with my observations, but perhaps I am wrong. The only thing close that I've found is this video which seems to suggest a broken apex seal:
I took a video of the noise with the hood up in hopes that it'll help. The video doesn't do much justice to the level of the noise as my phone seems to have automatically adjusted the volume shortly after the noise begins:

So, did I really blow a seal, or is it something else?

I know this may sound insulting, I once had that same misfire code from poor oil lubrication. Check the oil and see what you got!

I was using a 0W 40 it was very cold outside... Smoked out the whole highway, found it had gulped some oil through the throttle body, easily solved with a catch can.

The oil seems fine. I cleared the misfire code, and it hasn't come back, so I assume the misfire occurred during or as a result of whatever initially broke. It turns out the sound is always present, but increases in volume with revs (almost not noticeable at idle, quiet around 2k, starts making a racket around 3.5k). Using a stethoscope, I believe I've narrowed down the noise to the actual engine core itself. Something must be knocking around in there. Maybe the rebuild I got was at the limit of tolerances?

Since its still under warranty, I'm gonna have the dealership take care of it. Unfortunately I think that means I won't know exactly what went wrong.

Sorry to hear that, but if definitely take advantage of the warranty and let us know the diagnosis from the dealer

Nothing confirmed yet. Dealership has about a half day into it. Apparently the two techs that looked at it concluded that the sound resembles rod knock, but of course there are no rods to speak of. The techs contacted the Mazda tech line for assistance, and Mazda requested a recording of the noise. I'm guessing it'll be another 24 hours before I get anything more.