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I'm not going to agree with this being a normal occurence. My fl 8 slt has never made a screeching sound or sudden shifting of readings and have never seen another one do such a thing. I'd get on the phone with Vexilar people. It sounds to me like you have a unit that will have a very short life span. Mine is over 15 years old still going strong and still steady and nearly totally silent. I don't think yours is going to make it anywhere near that long. NBG