Idle Noise
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Both drives are very silent. However, the EG is the best.
Its not a big difference in the noise level, but what is more important is that I like the noise from the EG better than the GP. The GP has a noise that is higher in frequency vs the EG. Its almost like there is some metallic bi-noise in the "swoossshhh" sound from the platters rotating which the GP has, but is not there on the EG.
In a way, it reminds me of difference of the rumble of some old slow spinning 5 1/4" drives vs the whine of a modern 15k 3.5" drive.
The EG is a clear winner in my ears although the difference in terms of dB's is probably very small. With my fridge making some humming and light rain outside. I start hearing the GP 70-80cms away while I can clearly separate the sound of the EG from the ambient noise in the room about 60 cm away.
In terms of vibration, both drives are good, but the GP is slightly better. I can barely feel the idle vibration of the GP sample I have if I hold it in my hand, I can feel it on the EG.
I pulled out a WD5000KS for good measure and its not even a comparison. Both EG and GP drives are way more silent and produces less vibrations.
In terms of vibration, If the 5000KS is 10 (most vibration) and the GP is 1(best) I would put the EG I got around 3-4.
On my TV table, the 5000GS will put a hearable humming sound in the table itself (the table hums easier and more than my P180 cabinet).
Neither the EG or GP make vibrations strong enough to make the table hum (at a volume that can be heard with my ears anyway) so I suspect the difference will probably not matter for a machine with 1 or 2 drives, but might make a difference if you have many drives.
Seek Noise
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I had AAM enabled on the GP and no easy way to disable it so comparison will only be with AAM.
Without AAM the noise of the EG drive is of course (?) much louder than the GP. It takes a bit work to get the EG really noisy though.
I was making a small shell script using a bunch of dd's reading at different offsets on the drives for this, and frankly I needed a few more dd's reading at the same time to get noise out of the EG than I needed on the GP, but once pushed hard enough, the noice from the EG is quite loud without AAM.
I have never heard this during normal operation like streaming a TV recording or copying a few hundred MBs of files, but maybe if it was the OS drive I would have heard it better.
With AAM, the noise difference is more difficult to compare. The two drives actually sound a bit different. The GP seems to have a bit louder clicks (real chunk like sounds) but less of them. Maybe something about how the drives order the reads or maybe its just a result of the USB interface not being able to put as much load on the drive as the SATA interface can.
From what I hear, under light random access, EG is best, but under really heavy load, the GP seems better (could be due to the USB interface)
In terms of vibrations, you can feel the seeks on both drives in the hand, but the EG seems slightly better (again, might be the result of more aggressive reads there due to the SATA interface allowing more commands/sec which again could make things feel different).