Colorado noise at 2000 RPM 1600RPM and 1200RPM

When I reach these RPMs and stay at these RPMs and a little at idle an annoying fan vibration type noise comes from my engine or torque converter. Has anyone else had this problem? I have an 04 colorado with the I-5. I bought it used with 24,000 miles on it. It made the noise at 2000 rpm only until last week when it started elsewhere. The truck has 71,000 miles on it now.

I also have a 2004 Colorado with the 3.7L I-5 and an automatic. I just noticed this noise today, like a off balance fan. It happens at 1600 RPM and 2000 RPM when warmed up. More noticeable when in drive. I can get it to make the noise in park but it it was harder to make it happen the longer it sat there. As soon as I put it in drive, it comes back at those engine speeds, regardless of gear.

Any solutions?