Seagate 7200.8 vibration inconsistencies

[One]

I got 6 Seagate 250GB 7200.8 and they vibrate a different amount when idle, there is a big difference between the drive that vibrates the most and the drive that vibrates the least. I have all drives resting on foam.

I measured the vibrations with my sensitive finger at the same spot on each drive.
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Vibration estimation %

Seagate ST3250823AS

RAID 10

Drive1: 75%
Drive2: 40%
Drive3: 100%
Drive4: 35%


RAID 0

Drive1: 80%
Drive2: 80%


Samsung SP1614N (Nidec): 60%
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Is this normal or should I RMA 4 of the drives or only 1, or none? (I don't want to waste money on shipping, with my dealer I need to pay it myself.)

Will the harddrive fail sooner because it vibrates more?