97' Expedition XLT?

My mother has a 1997 Expedition XLT 4x4 with the V8 4.6L engine. and she says it gets kind of loud going up hill or when there is a pull on the engine. i asked her to elaborate and she says it gets loud from the engine
not from the exhaust. i was confused so i drove it for a little while and going up hill it does get rather loud, like the intake is having a hard time pulling in air. this isnt an exhuast sound. its defintly under the hood.
Anyone have an idea?
DJ TecThreat

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