Some 2016-2017 Ford Mustang GT350 vehicles equipped with the 5.2L engine may exhibit a rattle or rapping type sound during cold operation at light loads and speeds from idle to 3,000 rpm. The noise will be most noticeable during light acceleration in the 1,500-3,000 rpm range and may also be noticeable in the 800-1,200 rpm range with neutral throttle blips.
This sound is caused by the piston motion in the cylinder bores. This is an inherent characteristic of the forged aluminum pistons utilized in the high performance engine. Once the engine reaches operating temperature the noise will diminish. According to Ford, “there are no durability concerns with this sound.”