I,ve had several of the LA 40 and 46's. The black plastic Master Airscrew props do make alot of noise on this engine for some reason, try a Wood Master Airscrew or an APC. Also, another rattle noise comes from the crank endplay. I have had good success with making paper shims or washers and installing them between the drive hub and the motor. Install the shim and tighten the prop then check the play, if it drags make a thinner shim, if it is still loose add a shim, Add shims till there is no play and it turns free. The paper shim(s) have lasted me over 70 flights and really quiets the motor.