Acousto-optic modulator (AOM) plays an important role in heterodyne interferometric sensing, and it is always regarded as an ideal optical frequency shifter. For the first time, we compare the effects of its residual zero-order diffraction in different AOM configurations. The theory shows that using double AOM can effectively solve the same frequency crosstalk problem caused by zero-order perturbation without worsening the noise floor. The interferometer employs photonics-assisted-mmWave composed of two comb lines from an electro-optical frequency comb as the optical source, which results in the laser frequency noise cancellation in the difference. Experimentally, a dither with a peak-to-peak value of 0.15 ps in the single AOM configuration can be effectively suppressed to below the noise floor through double AOM, which shows the potential to achieve high sensing accuracy.