I have a DEF33 electric fireplace. I t makes a loud screeching noise when we switch it on. It appears to do this only when set on a low setting. Sometimes we put it on and it doesn't make the noise until it's been on for a while. It does throw heat. Do we need a new fan? It kind of sounds like an elephant. When it's been running and starts to make the noise, and then stops the noise, the heat also stops.