07 diesel Rodeo humming noise at 1700rpm

Hi All,

I have a 4wd common rail Rodeo 2007 model which is beginning to make a humming soft vibration noise when the revs are between 1600 - 2000rpm. I can feel it very slightly through the accelerator pedal, but the vibration is very dull. Has anyone got any info as to what it may be?

Thanks,

Ruddeo