Car makes a whining noise when accelerating?

I have a 06 Honda Civic every time when I accelerate the car makes. Whining noise the noise it starts after I drive the car for like 2-3 minutes.doesnt stop till the car is cooled off. A mechanic told me it was an exhaust leak?anybody know what is could be? I can cruise down the highway without touching pedal but when I press on it it makes the noise

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