2005 Dodge Ram Idler wheel

The bearings in idler pulleys usually make a buzzing noise. A tear on the serpentine belt could make a ticking noise, but you already noticed the most important clue; it only happens under acceleration. Idler pulleys and serpentine belts don't know or care how much load the engine is under. Any noise they would cause would still occur while you were poking around under the hood.

What you did a dandy job of describing sounds exactly like an exhaust leak. You might be able to make the noise occur by holding the brake applied, standing still with the truck in drive, then press the gas pedal to put the engine under load. Your mechanic would do the same thing with a helper inside the truck while he inspects the exhaust system.

Typically this type of leak occurs between the exhaust manifold and engine or between the manifold and exhaust pipe connection. Although it's possible, rust holes in the muffler or pipes don't usually cause a ticking noise.

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