Buzzing Noise at 1600 RPMs

I have an '09 v6 automatic with 75k that makes a vibrating/buzzing sound just over 1500 rpms, right about 1600 RPMs. It makes the noise during acceleration and when driving at a speed in that rpm range (for example when driving at 35mph). If i accelerate through that rpm quickly it doesn't seem to make the noise at all, it's worse the slower I accelerate through that RPM range. Everything else seems to work fine, I've meant to take it in to have it looked at, but haven't found the time. Anyone else have this problem, or have any ideas? Thanks!