Ah - this is true it can depend on the drive. The biggest variation tends to be in the loudness of the 'clicking' as the head moves. Older SCSI drives were (in)famous for how loud that could be. For the most part it's a light hum of the motor. In my systems the case fan's are much louder though. I suppose it's a personal preference.

It's generally at the "whisper" level or lower. But thinking about it being in my living room I could see it potentially being an annoyance compared to a silent drive. Depending on where it is, how enclosed it is, etc.

I have very recently acquired 4x18TB Seagate Exos drives for a fresh server. I parked them in an old case I had lying around where i was barely able to secure them all with screws, and cooling was especially problematic. Noise was horrible. standby noise was already audbile in the entire room. and when writing data while parity calculations were running, you could hear it in the entire apartment. The noise travelled through the wooden floor into every other room.

I have now moved the server and the drives into the fractal define 7 case. the drives rest on specially made rubber bearings that came with the case. the sides are noise isolated. the system is running with 6 fans total, 3 of which are 120mm corsair fans repurposed, and 3 are 140mm from the define 7. the server is now close to noiseless. vibrations do not rattle the case as with the old one. the rubber bearings isolate most of the vibration anyways. all that is left is a bit of head clacking, which gets isolated away from the case sides.

long story short: the drives are only half the story. you need a proper enclosure that is noise isolated. the define 7 is comparatively huge, but it gives you immense room to grow and was truly a godsent regarding noise.

I have a bunch of WD HDDs (9) in my Fractal Design Define R7 case sitting on top of my desk, about 2ft away at ear level, and can barely hear them. If anything the hum of the fans is what I can hear most (though still quiet). I have a security camera NVR with a little 40mm fan 12ft away on top of a high shelf in my office and I can hear it over my server by quite a large margin.

Even if rebuilding it today, I'd go for HDDs as you can't buy 12, 14, 18TB, etc SSDs for a couple hundred bucks and you won't really gain any benefit using SSD over HDD as reading large movie files from a disk isn't going to saturate the drive cache and you won't be dealing with random seeking.

You said you might upgrade all the drives in the future but how (2nd NAS?) and what will you do with the old ones? 4x4TB is going to fill up pretty fast especially when you're first starting out and eager to add new titles.

WD Red are the quieter you can find and they can spin down if you configure them to do so. Seagate Exos drives are the most loud and annoying drives you can get, they won't also spin down no matter what you set their config to.