The furnace on our new 337rls make sounds like it's not igniting, like a loud roar that shuts off after a couple seconds then a fan type sound then the roar for a few secs and so on until eventually after a minute or two and we raise the temp setting it goes on with a constant roar type sound. To me the roar sound is what I'm used to from my old rv but I've never heard my old furnace sound like it s having a hard time lighting. Does that sound normal to anyone?