Roque, do not think I am flaming you but it is unlikely that three could be defective. I figure that they are just new and need some use. Of course, yours may well have had a problem and I certainly hope the new unit works out for you. My tractor makes all kinds of noises, most are swishing, whirring noises and whinning noises. Someday we will have to get a manual on these things and study up on what goes on in their inards that contributes to the assemblage of noises. The 7500 I demoed made about the same noises by the way, it kinda made a tick, tick, tick sound whereas my BX goes tock, tock, tock /w3tcompact/icons/smile.gif . Take care, my fingers crossed for you. J