Is it just me...

or does the Merlin in the Acceleration Mustangs sound like someone left a rod loose under the valve covers? I've heard several Merlins and I don't think I've ever heard one like that. :P
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I'm not too sure about the meaning of "rod loose" (I'm not native english), however if you are refering to a strange noise, it may be because you have damaged your engine !
The acceleration Mustang had in-built engine damage, if you push the motor a more than 50% of power the manifold pressure will go past the red zone, and after some seconds (it's really quick) the engine sound will change, and after a short while the engine power will decrease, and smoke and flames will eventually appear.