I just bought this HDD in order to replace a Samsung Spinpoint F1 1TB and a Hitachi Deskstar 7K1000.C 1TB, because they were quite high on the power on counts, with 42K and 30K hours respectively, and also because they created a beat frequency when powered on, and seemed to make my Windows 7 Pro 64-bit bug when shutting down the PC, as I use the option to turn off HDDs after 1 minute of inactivity.
To be fair, I'm not 100% sure my Seagate Barracuda 3TB is the same version as the one tested, as it's a STD3000DM001-1CH166 according to CrystalDiskInfo. But my observations are that it emits a very-high pitch noise when powered on, probably some noise associated to the spindles spinning ; I tried to get a sound spectrum with my headset's mic and UltimateSound 2, but it's hard to pinpoint what's the whistling I can hear. Here are the spectrums I get with the microphone (for which I don't know the frequency response) touching the front bottom of my PC when idle, with the HDD writing some data though that doesn't affect the whistling :
The first spectrum is from 0 to 1391.6 Hz.
The second one is from 0 to 22265 Hz.
The biggest peak, that is highly visible on the first figure, is the HDD's rotation speed at 120 Hz. The remainder of the spectrum seems to be some broadband noise, but for some reason, my ears can hear that high-pitch whistling. I should remark that this whistling is probably not disturbing for most people ; it's less than the whining my TV does when turned on. And while it does make more noise than the PC's fans and watercooling when idle, those are 1 140mm fan at around 500rpm, 2 120mm fans at around 500-700 rpm, 2 80mm fans at around 1000 rpm, and a Corsair H90, which does make a slight ticking noise caused by some air bubbles, all placed in a Corsair Carbide 300R recovered with a decent amount of soundproofing material, especially around the HDD cage.
The bottom line is while this HDD is probably one of the quietest 7200 rpm HDDs on the market, it does produce some high-pitch whistling that can disturb people highly sensitive to high-frequency noise.