I was working on this model fireplace last week. The gas company was out and left a note with the homeowner saying that it needed a new gas valve. When I got to the call, I found that the unit was slow and erratic to light up, and that the pilot had to be lit by hand because the sparker was broken. When I turned it on, it made a loud metallic fluttering sound. I tapped on the valve and the burner, but could not stop the noise. I proceeded to replace the gas valve and pilot assembly, and now it lit promptly when the switch was flipped, and the pilot stayed on. However, it still made the noise, even after I adjusted the primary air shutter open and closed, and had cleaned the burner orifice several times. I have never worked on a fireplace - I just got sent to the call, and accepted the challenge to try to fix it, even with no experience on them at all.
Anybody ever hear of this?