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Discussion Starter · #1 ·
94 caprice 4.3
faint humming sound coming from under the hood
happens when idling or driving.

alternator was replaced about 3 or 4 weeks ago.

any ideas?
 

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Does it happen all the time, or periodically, especially just after starting the car? If all the time, you might want to start replacing vacuum lines and the PCV valve if it hasn't been done in a while. If mostly after starting the engine, could be the AIR pump starting to make noise.
 

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the electric air pump operating
 
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