2004 1/2 ram 3500 4wd

[rk59405]

My 2004 1/2 ram 3500 4wd recently started making a kind of buzzing noise starting at 2200 rpm (gradually then getting louder) and stopping around 2700 rpm. Speed or tow/haul position make no difference. Buzzing seems like coming from dash forward ( put hose to listen under dash but could not pick up source). Only does it while driving down road so hard to troubleshoot. 118,000 miles on truck, no modifications. Any help would be appreciated, Thanks Rod