Hi, I have a 1TB 7200rpm drive on my PC as the main/only drive.
I use a Scythe Quiet Drive, which I think is very good. I also have it sitting on foam so it's decoupled from the system so no vibration is transmitted or amplified. When SPCR tested the 2.5" version they found it to take 3-4dB(A) off the drive's noise level, I can easily believe the 3.5" version does the same.
I've used a WD Black, Samsung F1 and Samsung F3 all 1TB at various times. The WD is significantly louder than the Samsungs which are very similar. The F3 has a touch of high pitched noise about it that the F1 doesn't have but the SQD removes this.
I did a side-by-side comparison of WD black in the SQD vs the Samsung F1 bare. The idle noise was very similar in level, I don't recall about seek noise. According to SPCR's measurements
this means the 3.5" SQD is good for 4-5dB(A) reduction in noise. If this is the case then the ~16dB(A) Samsung drive is reduced to 10~12dB(A), which is similar level to SPCR anechoic chamber. I.E. very quiet.
I live in rural location and even at night when I can't really hear anything I don't find the hard drive to be intrusive in anyway. Maybe it's masked by the rest of the PC but idle the 80/92/120 mm fans spin 700/620/530 rpm so no exactly loud.
The problem is the SQD is quite a lot of money and 1TB 7200rpm drive + SQD isn't much cheaper then 1TB 5400rpm drive + 40~60GB SSD that will be equally quiet and much faster solution.