Hi,
This is just to document a problem that I have experienced. I did google for it before but did not hit on the right solution. The dealer has fixed the problem, now. I just wanted to share my experience so others can have an easier time in the future. This is also to see if other people have had the same problem.
I have a Camry 2005, and it started to make some noise about 1 month ago. At the begining it was just some minor humming sound. But it got louder and louder. Here are some characteristics:
(a) The noise only depended on the speed of the car: the RPM (tachometer) did not matter, in fact, one could shift to neutral while running and the noise would remain.
(b) The noise was resonant in nature: the noise level peaked at around
44 MPH and 66 MPH, I speculate that there might be yet another peak at 88 MPH, but I never drove that fast to be able to check it. (The actual numbers should be 45 MPH, 67.5 MPH and 90 MPH, but I guess no one would believe me I could pin-point with such a precision... so I rounded them to 44, 66 and 88 to help mnemonics. I mention both sets of numbers here just to help people Google in the future.)(c) The noise got louder with time, and the resonance peak spread. Originally the noise was confined to around 44 MPH and 66 MPH, but later it spread to other speed ranges as well, while retaining the resonance peaks at 44 MPH and 66 MPH. The noise is accompanied by minor vibration of the car (one only feels it at the gas pedal.)
(d) The first mechanic suggested it might be the tires, and indeed I saw a tiny bit of wear in inner edge of all 4 tires. He did rotate the tires, but the problems remained. I asked him whether the problem could come from the wheel bearing, he said it was not likely for a Toyota under 100K miles. I re-checked the tire pressure (recommended at 32 psi) and all tires had good pressure.
(e) I took it to the dealer, and they indeed diagnosed the noise as coming from a faulty wheel bearing. Since the car was still under warranty, they replaced it free of charge. They had to special order the part, though.
(f) The day before the dealer fixed it, I also realized that the noise level was asymmetric when turning: louder when one turns in one direction on a curve, quieter when one turns in the other direction.
The cars runs fine, now. No more noise.
Lesson? Despite the brand name, problems can happen at the factory level. Early diagnosis and early resolution may prevent long-term damage. I know noises are one of hardest problems to pin-point: noise can come from everywhere, and many people complain about different kind of noise. But clues like (1) independence from RPM, (2) resonance characteric, (3) left-right asymmetry, etc. should have helped me to pin-point the problem faster, I just was not lucky when I did the Googling. I hope this message helps others. I have now been able to see that from other Google postings that wheel bearing problems indeed have these characteristics I have described.
-- J.