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I'm driving a manual 96 Toytota T100, and recently the engine started making a high pitched, almost inaudible whine. Some things I've loosely figured out:

  • It always stops when the brakes are applied, but doesn't stop for the clutch
  • It seems independent of speed or revs
  • It sounds cyclical with a slight random component, and fades in and out as I'm driving or stopped, but will usually go for 30 seconds at a time
  • It seems independent of the heat/ac fan speed
  • It seems temperature independent (both outdoors, and how long the truck has been running)

Any ideas where to start looking for the problem?


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From your question, the whine is linked into braking both when the veicle is stopped or moving. I would first look at the brake servo, its hoses and valves. A vacuum leak can give a whining like noise.

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Also called the power brake booster, it has the master cylinder bolted to the front of it and mounts to the firewall. – mikes Nov 22 '13 at 23:24

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