My Tacoma has been making a strange revving and rattling sound when the truck is in motion and the brake or the clutch is pressed and the gas pedal is released. I couldn't reproduce the effect when idling. I first thought it might be the heat shields around the exhaust assembly as it feels that's where the noise is coming from but they are all pretty firm. Doesn't feel like it's coming from the engine itself. The noise is sort of like as though something is stuck in the way of either the fan or the drive belt, which I inspected negatively. It does not happen every time.
Any pointers where to start looking?