Noise is a critical parameter for electrified mobile machinery. Both electric and hydraulic machines generate periodic forces that excite the surrounding structures and generate noise. This paper discusses harmonic orders and their origin in hydraulic pumps and permanent magnet synchronous motors (PMSMs). By combining the pump and motor, the harmonics of both machines interact, and the noise experience changes. This must be taken into account when designing electrically driven pumps. The effect of the combination of the design parameters; number of pistons, number of slots, and number of poles on the system harmonics is discussed. Traditionally, hydraulic pumps use odd piston numbers to reduce noise. However, if identical numbers of poles and pistons are chosen, the pump and motor harmonics coincide and can interact constructively or destructively. This paper shows, using torque ripple as an example, that selecting odd piston numbers is not straightforward when combining pumps with a PMSM.