Locate the pilot by using a flashlight and peering inside the firebox with the fire turned off.
Look for the flame on the pilot. Underneath the pilot valve is the screw that controls the height of the flame.
Turn off the gas source to the logs by using the gas key to turn the valve clockwise.
Read the owner's manual to determine the correct height for the flame.
Twist the screw with a screwdriver to raise or lower the flame to the height recommended by the owner's manual.
Turn on the gas source with the key and start a fire to determine if the noise stops.
Turn off the gas source to the logs by using the gas key. The key typically fits into a small hole on the exterior end of the fireplace or up near the mantle.
Locate the tubing that forms the fuel line, which connects to the bottom near the pilot light valve and where the flame comes out.
Twist the fittings off the fuel line, using wire pliers to turn each one counterclockwise to remove.
Buy aluminum or copper tubing the same length but with a larger diameter than the fuel line. Often the whistling noise is caused by corrugated tubing that isn't smooth inside the tube. Replacing corrugated tubing with smooth aluminum or copper tubing often fixes the problem.
Ask for fittings that work on the larger diameter tubing.
Repair noisy whistling by installing the new tubing and fittings, using the pliers. Slip the fitting on one end of the tubing over the open section where you took off the smaller one. Tighten the fitting by turning clockwide with the pliers. Repeat with the other end and fitting.
Turn the gas source back on to use the fireplace.