For the second time in about the same spot, my truck is making a wierd noise. Its almost at the top of a really long steep hill. Under hard accelaration a loud very sharp whisle will start from what seems to be from the left side of the motor. Pretty much right under the dash in front of the steering wheel. If I let up at all it stops. Its at about 3/4 of the way thru a 250 mile trip. The gauges all read normal and the truck runs the same before, during and after. Its a 04 6.0 without any mods except high idle. The oil cooler was dealership done in 07. It happened when the oil change was due(about 4000 miles) and about a month after a service.