Whats this noise

I have a '96 mazda protoge and i have an odd noise at 27-2800 rpms. Its like a metalic rattle( for lack of a better description). Its a manual trans and if you rev up to say 3200 quickly then shift its almost unnoticed, but if you go through that rpm range slowly or are staying in that range its quite loud. The noise is only at that rpm range

Might be a heat shield that has rattled itself loose over the years. They tend to resonate at certain engine speeds. Peek around under the car in the header/muffler/cat area to see if anything is loose.
If that’s not it, you could get a cheap automotive stethoscope and probe around.

Does your protege otherwise work well?

I have a '03 Protege5. I have noises I wonder about though if adjust my driving, I don’t hear it anymore. Sounds like you can avoid the noise.

Otherwise, I like the idea of looking under the hood. If the car is working well otherwise, it may be something simple to fix. It may really be something loose that’s resonating with that vibration/rpm.