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Camry auto transmission humming noise when I accelerate from a cold start

When I first drive it in the morning I get a humming noise when I accelerate from a cold start down the alley in back of my apartment. If I let up on the gas pedal and then press it again I can stop & start a repetition of the noise.
SPEED: Less than 20 MPH

If I let up on the gas pedal, the noise stops – which for me eliminates a lot of causes.

Another clue is that once my Camry warms up the noise seems to go away.

It’s a 2006 LE, but has less than 80K miles.

Your thoughts.

The noise you hear might be as simple as a loose exhaust heat shield making noise when the exhaust is cold.

Then when it heats up, the noise stops.


Could be a serpentine belt problem too. This is a common way they act up, b/c the belt is longer when it is cold so it is able to slip more easily. Rubber shrinks when it warms up. However, the noise these belts make tend to be described more as “squeals” rather than “humming”, but if nothing else pans out, worth considering.


Doesn’t the serpentine belt tensioner make up for that?


According to this website, even w/a tensioner in the loop a shorter belt will have higher tension. How much higher, depends on how short the belt is cold vs warm I guess. There’s also the factor of belt stiffness when it is cold.

  1. Belt Length Matters

Replacement belts must be close to the same length as the original. Low-quality replacement belts may not be the correct length and will push the tolerances of the tensioner. A belt that is too short, for example, will cause too much tension and put higher than normal loads on the bearings inside the alternator, power steering pump and water pump. A belt that is too long (just an inch or less) may slip, make noise and wear prematurely. It will also cause the tensioner to work harder and fail sooner.