Well this thread got interesting
The hissing sounds like a coil whine issue to me. It affects pretty much everything. I saw nothing but complaints about it when researching Dell XPS laptops, which seem to have gained it as a reputation, bought a Lenovo (for other reasons) and that has it a bit as well. One of my previous justifications being something of an Apple fanboy myself until recently, would've been that Apple hardware just doesn't suffer from that kind of problem as they pay too much attention to the user experience. And indeed, were Steve Jobs around, he'd say "this thing is hissing at me?!", lob it into his fish tank and tell the engineers to GTFO and not come back until it's not doing that any more.
This is an example of why I've given up with them - it used to feel like I was paying more (both in money and in sacrifices like customisation, certain ports etc) for a better quality and cutting edge product. Now you're paying more for nothing all that special and giving up the quality as well. If I'm going to have all the little quirks like coil whine etc anyway, then I might as well pay half the price for Windows and Android machines.
As for worrying about how to minimise battery wear, I've been there with that kind of thing and come around to "just don't worry about it". With all the intelligence they put into charging and power management I think you'd have to really actively abuse it - like a pattern of 'play a game draining it as fast as possible, immediately charge it, immediately play game, repeat' that goes on all day every day - to wear it out much faster than average and make much of a difference towards the end of the product's life.
Honestly when you get all OCD about that kind of thing where you practically revolve your life around optimising it you just end up missing out in other ways because you're too worried to use it to its potential and it effectively only has 60% of its battery life from the very beginning because you daren't let it drop past 40. Just enjoy the tech you paid £700 for and put some faith in the experts who control the power management stuff. Life's too short.