Honda has a technical service bulletin regarding this for the Accords with the L4 engines.

Note: Technical service bulletins are not recalls, unless specifically noted as related to a recall; generally, they are to help Honda technicians with known issues. Issues noted in TSBs do not necessary apply to all vehicles. Normal warranty applies.

Honda TSB 12-085
Buzz Coming From the Engine Compartment After the Engine Is Turned Off

Applies To: 2013 Accord 2-Door – From 1HGCT1...DA000001 thru 1HGCT1...DA000123
2013 Accord 4-Door – From 1HGCR2...DA000001 thru 1HGCR2...DA021824
2013 Accord 4-Door – VIN begins with JHM

SYMPTOM
Buzzing is heard coming from the engine compartment after the engine is turned off.

PROBABLE CAUSE
The PCM operates the VTC solenoid with the ignition key turned to the OFF position.

CORRECTIVE ACTION
Update the PGM-FI software in the PCM.