according to my observation the problem is in IAC valve , definately high RPM(speed)is responsible for loud engine sound. ur IAC valve needs some cleaning.
for ur information here is some IAC valve info :
An IAC (idle air control) motor is designed to adjust the idle RPM speed by opening and closing an air bypass passage inside the throttle body. The computer or ECM (electronic control module) receives information from various sensors and will output signals to adjust the IAC motor in or out to adjust engine idle speed by controlling idle air. An IAC motor can fail one of two ways, either the motor short circuits and stops working or the motor will develop high resistance and cause the IAC control motor to react slowly, either failure can cause the engine to stall at idle. When a trouble code scan is performed it sometimes won't always detect a failed or weak IAC motor. To check the IAC motor remove the unit, with the wires connected turn the key to the "on" position without starting the engine, the IAC should move in or out. If the IAC motor does nothing it has probably failed, replace it with a new unit and recheck system. Note: while the IAC motor is removed clean (use aerosol carburetor cleaner) the passages the IAC uses to control idle air speed, also inspect the IAC for a build-up on the seating (pointed) end and clean as necessary.