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Hello, my sister just got a 93 legacy wagon, and when you switch the heater to a defrost setting, it makes a rattle noise, which seems tied to the engine speed. It seems to go away as you go faster, but then it will come back. Any Ideas? She JUST got this car, so I haven't been able to poke around yet. Any suggestions would be great. P.S. My car is a 85 Tercel wagon, which is what's in the avatar.