My 2012 F150 FX4 5.0 Coyoto is having a noise issue from under the hood. I am having a lot of service done to this truck. So far I had all of the coolant flushed and serviced with new thermostat and proper coolant and spark plugs as well. 134000 miles. New strutts and rear shocks, transmission and drive service at Ford dealership. New belts and tensioner and idler pullies. After this there is a sound that sounds like a belt slipping and goes up or down with the engine rpm. When the mechanic did the belt change he noticed it and used his stethascope and cound not determine where it was coming from. When I am standing in front with the hood up and listen to the noise it seems to be coming from the passenger side, front of the engine. It is very cold here so I could not spend too much time but is there a bearing going bad in whatever is on the front of the engine that would sound like a belt squelling? I am a plumber so my knowledge is limited.