2017 Toyota Highlander Owners Manual - Page 8 explains the sound well - "Approximately five hours after the engine is turned off, you may hear sound coming from under the vehicle for several minutes. This is the sound of a fuel evaporation leakage check and, it does not indicate a malfunction."
Went into the garage and heard humming noise coming from underneath car, towards the rear. Car has not been driven for 5 hours. Sounds like a fuel pump running or an air compressor. Car is off. No lights are on. This is the 2nd time we have heard this. Will contact dealer.
A D V E R T I S E M E N T S
Went into the garage and heard humming noise coming from underneath car, towards the rear. Car has not been driven for 5 hours. Sounds like a fuel pump running or an air compressor. Car is off. No lights are on. This is the 2nd time we have heard this. Will contact dealer.
- J G., Bowling Green, OH, US