Car Hums before shifting gears?

I have a 1999 Ford Escort 2.0 DOHC 4 CYl, manual tranny, and I normally shift at 2.5k rpms, but lately when I hit about that RPM or higher, the car sounds like an angry cow, or like a plane flying overhead. It goes away when I slap it in neutral. Thoughts?

Whenever I hear about humming at a particular RPM, I think of loose, vibrating heat shields or exhaust flanges. Put it on a lift and check. You’ll either find the problem or rule it out in about 30 seconds.