Hello gurus,
Anyone can explain the two time calibrations of newer models of WD drives, you can hear the drives (500GB and +500GB) makes a normal calibration sound then they act like they will spin down then the motor speed increase again and makes another calibration.
Sorry for my bad english.

Any explanition will be appreciated.

If spin down , that should be means physical problems, maybe MHA, WD has some tendence to Head Crash so should be checked before too , if its Green power tech, this models are more quiet than olders version so recalibration sound its not easy to heard

I've seen cases where it seems as though the heads are bad, but when I ran tests on the PCB I noticed voltage irregularities with the motor controller chip. After changing the chip the drive was accessible. Not saying that's what is wrong in your particular case, but it may be something to look at.

Intermittent inaccessibility or permanent ?

Bad Head.

I was concerned about the bad controller that made the disk unstable... So I asked if it was (in that case !) intermittent i.e. thermal-related OR permanent.
About the original case (OP posted) everything can be, but it makes think about ONE head - not relevant for startup - failing.

Thanks for answers,
Mr.BlackST: the drives are working fine, no physical or logical damages Mr.Beto
My question is : when you listen carefully to those drives (blue, green and black) capacity from 500GB and above they makes two calibrations sound.
Sorry, my english can't help me to explain.
thank you all

Regards,

As Alberto said, in those newer drives, it's not really easy to hear the calibration sound perfectly. I may have to do it sometimes with a stethoscope. However, it may only be your theory that the drives are physically perfect?

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Bitlevel Data Recovery

It's not a theory, it's a fact that the drives are physicaly and logicaly working fine
Thanks for all answers.

Best regards,