I've got a 2013 Hyundai Accent with a noise coming from somewhere under the hood. Happens only at a fairly narrow band of engine speed (1100-1200 RPM). I've been trying to hunt around for the source, but I'm running into an issue: Since this car has a drive-by-wire throttle, there's no obvious way for me to bring the engine up to the speed required to hear the noise.
On my other ('94) car, I can just grab the accelerator cable with my hand and goose the throttle to my heart's content. On this car, the throttle body is buried under a mass of plastic covers, sensors and servos, and I'm pretty sure that even if I did manage to manually move the throttle plate I'd just make the ECU angry.
So what's the solution? I don't have a helper to sit in the driver's seat and give it gas while I listen, and any methods involving the ODB port seem to involve a lot of reverse engineering and experimentation.