Drone like low noise at 2000 rpm

I have a 2003 Tacoma TRD extra cab 4x4, 3.4l engine with 113K miles. There is a low droning noise at 2000 rpm which stops when I take my foot off the accelerator. I have experienced wheel bearing failures in other vehicles and this sounds very similar but does not change when swerving left or right and appears only at 2k rpm and above at highway speeds. I am wondering if it could be a bearing in the engine since it stops when I lift my foot off the gas. (cam shaft or crank shaft bearing?) Timing belt was done at 110k with new roller and tensioner. I have searched the forums to find a post of similar complaint without any luck and am hoping someone here has had the similar trouble.

Thanks.....

 

Should anyone have something similar; changed the center carrier bearing and all four universal joints and noise is gone. Sure sounded like the sound was coming from the front but a vibration on the floor that came and went with the noise tipped me off.