This morning on my way to work I was doing maybe 70 and I accelerated to pass some traffic. I accelerated hard enough to make the tranny downshift into 3rd. When I did this the RPMs climbed to around 4000 (or more; can't remember) and I started hearing a rattling sound - almost like a heavy whirring sound. I've never heard this noise before.

At first I thought it was my heat shield but I've heard those before and this was a rapid steady rattling (almost like a whirring) - whereas a heatshield would not sound as steady as this (would sound more broken up)

I did some research on the org and found out that people say it could be either the maf or coil packs failing.

However, those people experienced loss of power, crappy milage, and hesitation upon acceleration and while their engine was cold. I am NOT experiencing any of this - matter of fact, the car still feels as strong as new and I still get great milage and the engine has already been warmed up for almost an hour of driving at about 25-40 mph.

And lastly, the sound stops immediately when i release the gas

If anyone can shed some light on this I'd greatly appreciate it.

Thank you,