Another noise question - transmission or engine

This board has been great. I have owned the car for only 3 weeks, really like it but there are certainly a lot of quirks and people have been great sharing information.

This has happened twice in the three weeks. I am driving normally in city traffic, come to a stop sign and put in in neutral. Loud whining coming from engine or trans. When I rev the engine the noise stops above 2,000 rpms, comes back below 2,000. I drive it a little longer put it in neutral and noise disappears - normal or serious. Thanks.