I thought I would come to this thread to ask. I purchased a new 2017 iMac, spec wise, it has 3.5GHz Intel core i5 CPU, Radeon Pro 575, 8GB RAM and 1TB fusion drive, so it's the mid configuration out of three available stock options. I've noticed this issue on my outgoing late 2015 iMac with similarly configured spec, with 1TB fusion drive, but I notice a little electronic hissing noice coming from the bottom left side of the computer when for example, watching a video off of YouTube, or switching applications, essentially like a hard drive clicking sound as it reads the data. however, I can distinguish the noise that's coming from a hard drive portion as it has more heft to the noise, but this noise that I can obtrusively hear when using it in a quiet room is is quite noticeable, even more noticeable then my outgoing 2015 iMac. I can't quite clearly describe the sound that I'm hearing, but it's almost like a computerized static hiss that I hear some how. Not sure what this is. I had a theory that it might be the SSd drive working, but it's quite loud and very noticeable to my ears on my unit. Does anybody else notice this too on your fusion drive equipped iMacs when it's used? It's quite subtle but still audible when the computer is in idle. Would love to hear some answers and see if this needs to be checked out, or if this something that I will just have to get use to with fusion drive iMacs. I remember hearing this hiss on my outgoing model but probably wasn't this loud so to speak.