1983 300D Turbo, 143,xxx miles:

I have an odd, loud problem coming from the instrument panel. Sometimes when driving, around 60 mph, out of nowhere a very loud wailing and "vibrating buzz" type noise comes from my dash, drivers side, sounds like it's coming out of somewhere between the speaker and the instrument panel. Every time it has happened, I've had the defrost on as well as the radio. When it first happened, I shut off the heat (no difference), then the radio (also no difference). The only thing that makes it stop is if i slow down to less than 30 mph and then resume normal highway speed. It seems to only happen once per drive, i.e., it doesn't come back when I get back up to 60 mph. There is no gradual build but there is a gradual decline as I slow down. Decline in volume and intensity. But when it first starts, it's immediate, without warning, and very loud. This has caused a couple mini heart attacks as well as pretty dangerous "jumps" of fright on my part. Worried with the winter coming and snow piling up, I'm going to scare myself and jerk the wheel or something ridiculous and end up in the ditch. Also, this typically occurs in the early morning on my way to work, in the cold. I start my car and give it time to warm up in the garage before I drive it but outside it's still cold in upstate New York. Any ideas, or is this just a ghost infested Benz?

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1985 300D - 1984 Euro 280E AMG Clone (SOLD) - 1978 280CE (SOLD) - 1983 300D (SOLD) - 1981 300D (SOLD)