I have an LP gas furnace. About 50% of the time when it lights, the flame travels back through the burner tube to the gas orifice.
When it does this it makes a raspy sound like when a oxy/ace cutting torch has the puddle blown back up the tip. Sometimes it clears itself. Other times you have to start over and it may light properly. Seems like there should be some type of cone or deflector to stop gas reversion back out the tube, but it's open and clear. If set pressure @ 11 in. and checked orifice size and both are in spec. Sorry for the long post but I'm out of ideas.