LOUD HUMMING NOISE.

  • Tiny
  • ZAKKATTACK
  • BMW 750Li

1999 BMW 750il with a 5.4 12 cylinder. I did a tune up on it and now after the vehicle warms up it's making a ungodly howling noise down by the torque convertor area. But when you let the motor cool down and start it back up it goes away until it warms up again. What can this be? Is it something I did or pure coincidence?

Friday, August 17th, 2007 AT 2:17 PM

3 Answers

  • Tiny
  • merlin2021
  • Expert
  • 17,583 posts

You might check for an air plenum problem.

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Friday, August 17th, 2007 AT 2:40 PM
  • Tiny
  • ZAKKATTACK
  • Member

So it might have a vacuum leak in the plenum? I'll definitely check that, but why would the noise be coming down by the torque convertor?

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Saturday, August 18th, 2007 AT 12:52 AM
  • Tiny
  • Dr. Hagerty
  • Expert
  • 9,709 posts

Could be the PCV valves on the back end of the plenum
(one on each side) it would make a sound like you described. To check this use a slack tube manometer at the crankcase, more than 6" of difference from side to side and that's where to start. Repost if more help is needed

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Sunday, August 19th, 2007 AT 11:09 AM

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