anyone heard of this? i searched the entire internet and didn't really find anything. after about 10-15 minutes of driving with the a/c on the expansion valve starts emitting a buzzing noise. it sounds like if you placed a sheet of paper into a running electric fan. it is not incredibly loud, but loud enough to hear over the blower. i've had the valve hiss when low on charge but this is new. the system works OK otherwise...

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1981 NA 300D 310k miles

Are you certain the sound is coming from the expansion valve and not the fan motor itself? A fan motor buzz would make more sense than an expansion valve.

Another thought would be the etr switch; again its in the same vicinity and could be on the threshold of opening and closing after 10 minutes or so. Does the compressor begin to cutout or chatter?
Mike

i'll check the etr switch. its not the blower though.

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1981 NA 300D 310k miles