HELP grinding noise when coasting

[dollabill840]

to start off my truck is a 98 xlt 4.0 shoc BW 4405 T case 8.8 rear end when Im driveing and coast at around 50 mph somtimes i get a grinding sound maybe kinda an eletric drill sound almost and if i just tap the gas it goes away every thing drives fine no hard shifting or rough rideing at all any idea please help

 

[marragtop]

Try putting it in neutral to see if it makes a difference. If so, may be trans related. Just a thought.

 

[dollabill840]

im kinda worried about driving it