RE: E-flight 370 outrunner problem.
It probably is a grinding noise... One or more magnets grinding on the stator...
I second Bevo's vote to send it in for repair. Even if you're not the original owner, Horizon will fix it, possibly for a small fee, possibly for free. It won't hurt to send it in and have them determine if it's even worth fixing. They'll definitely do that for free.