Well, wouldn't you know it, I got the pop this morning. I was making some stock for the week and had the pot boiling on a front burner while skimming the "chum." When I was done skimming, I moved the pot to a back burner to simmer and when I turned of the front burner, puff. From that point on it would puff whether simmer or high, slow or fast. As Trevor posted above, it had more to do with a hot burner and the extra gas. I guess I had always seen it before, but never thought much about it until this thread. One thing to take away from this is that when you do see the puff, there's no question that the burner is off.

Don't know if this will help but I have a vented propane gas insert and 4 days ago lit it .. pilot fine but burners wouldn't ignite. Just had my propane guy come look at it and turns out it's the thermocoupler (sp) needs replaced. Tried to get that "clicking" sound but no go. Didn't matter in my case that the pilot lite was strong. Just want to add the propane guy charged 125.00/hr rate so decided to get my faithful handyman to take care of it. Maybe it needs cleaning...that's what I hoped for but mine is 6 years old.

When you turn it to the on position, it requires the thermocouple to be fully heated or it will shut off. In my case, it takes WAY longer than 60 seconds for it to stay on. I mean it takes probably 3-4 minutes of holding the button in before it will stay lit. My fireplace the button for gas / adjustment of flame automatically is in the on position after I release the pilot process. I.e. I have to push and hold in the gas control knob to "pilot" light the burner, and when I take my thumb off the knob it pops out and goes to the "on" position. So my advice would be to hold the pilot light for several minutes and then release. If that doesn't work, then as noted you may need a professional to come look at it. Best regards.

The gas also seems loud to me. Assuming the link tool below works, what do you think? Yes, there is sound, and yes you have to turn the volume up a bit to hear what I am saying. Here is a link that might be useful: Gas Fireplace Sound