oahumiev, perhaps what you're referring to is the vacuum pump for the power brake booster? Most electric vacuum pumps I'm familiar with are awfully noisy, so I'm impressed if they've almost fully muted the sound and I don't recall hearing it at all on my test drive. I would expect to hear it for a few seconds at startup. In any event, it should be intermittent and also occur for a few seconds after significant braking (and not simply slowing down which uses regen which is what occurs when the brake pedal is first depressed).
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV