That sounds kind of odd. There is alot of vibration on deceleration, maybe something in your engine compartment is a little loose and the vibrations caused by the engine under decel are the same vibrations as the loose parts resonant frequency. Simply put the part will only be in resonance by vibrations caused by 3100 rpm under decel. Don't answers like this make life much easier?
> when i let go of the accelerator pedal from
> around 3500 RPMs the engine makes a buzzing
> sort of sound at exactly 3100 RPMs it only
> occurs at deseleration.could that be the
> timing chain? thanks