I got two of these from the one person, both we're external hard drives from different computers and ironically both are the same model with the same problem but manufactured about 10months apart.

HDD1 Spins up and Knocks does reach ready occasionally.
HDD2 Spins and knocks for 3 cycles before spin down.

I have done some head remapping to test the heads but still getting the knocking. Preamp fault on both i reckon. For a mha swap how much of the DCM do I need to match as unfortunately it seems impossible to get a complete match? I should be able to get away with the first 4 right?

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