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2007 Toyota 4 Runner weird noise at start up - Hums

First of all 230,000 miles.
Just began making a strange racket when started…sounds like a loud hum or fan running…right at the drivers dash. Thinking it might be the secondary airpump with leaking diaphragm goes away after 10 seconds…car runs great

Could be the ABS self-test activating. Another idea, an engine belt is worn and slipping. As rubber heats up it shrinks, and that makes the belt a little tighter after 10 seconds, which could stop the noise. Belt noise is typically referred to as a “screech”, or “squeal”, but might be described as a “hum”. A third idea, could be related to the HVAC system. Try turning it on/off, different modes etc, see if that has any effect.

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