'03 Mustang, V6, grinding sound at 2000 RPM



I have a 2003 Ford Mustang, V6, manual transmission, approximately 55k miles. For the last few days, I hear a grinding sound as the tach needle passes through 2000 RPM. The sound lasts for about a second. I don’t hear it at lower or higher RPMs. I haven’t heard the sound in neutral or in 1st gear, but I hear it in 2nd and 3rd. I haven’t tested 4th, 5th, or reverse. Any ideas?? Thanks!