"Uneven lighting on key 5"
Get a life ... each key is not EXACTLY the same with lighting, but pretty darn close.
The hinge is definitely a fault of Apple's, but this "hissing", I have NEVER heard about, let alone with 3 replacements in a row.
This one's on you, bud.
You're the exact type of person ruining the image of an Apple User - it's not Apple's fault, it's in your head (or headphones).

The OP also identified the hissing doesn't exist in the 15", why not get a 15" and be done with it? I've had 17" and 15" laptops and there's not a huge difference IMO.
Just to clarify since some of you just love to troll other people's problems.
The 4th MacBook Pro IS a magnificent machine.
About the Audio issue; The First MBP was way worse than all the rest. It was worse than the one in the store.
The second computer still had a small hiss. I didn't know this was normal since all other computers Ive ever owned and worked with (Network Admin, I work with a lot of computers) has never had this issue including my Black Macbook. On the second exchange, me and the Apple Genius were standing at the Genius bar doing google searches over the issue, and found that there are so many people having this same issue. He suggested that i buy the filter to raise impedance so i left. I have tried many different headphones/headsets on all of the notebook, so you can't hate on that.
For all who said I should have just been happy with what I had and all the problems I had were minor/ignorable are wrong. If you buy a brand new product, It should be perfect. If you buy a new gun, you expect it to shoot right, or if you buy a new car, you expect it to drive/look/feel right. Same goes to the computer industry.
As a PC user for most of my time and never experiencing an audio "hiss" in any of my notebooks, when i first got the MacBook Pro, I thought something was wrong with it.
Apple did do everything they could to help me out, but I do not see any way that I was out of line. I paid for the computer and I should get one without flaws.
I love apples warranty/replacement program and have always bought apple care since the first iPhone. (I'm an avid iPhone fan)
IMO apple is number 1 in support, but just like with anywhere, you can either get a person having a good day, or someone who could care less about your problems.
I think we all know how great Apples customer service is. Now for the techs, that's a different story. I damaged my new 2011 MBP within the first week during a business trip. Somehow the lower right corner got dented in. Genius bar was kind enough to order a new unibody case and have it fixed all within 3 days. Unlike the OP I checked everything before I left the store. I sat in the mall cafeteria and opened my MBP. Sure enough my 15" screen almost fell off. The hinge was loose and was making tons of noise. The screen was flapping around like sheets in the wind. I walked right back into the store and they fixed the screen. Apparently the tech forgot to tighten 2 screws under the unibody. The tech didn't even notice when he shut the computer. Even though they fixed my original problem for free, I still was a little pissed and wondered how a Apple technician can forget to tighten 2 screws and not notice it lol!
pissed, my £999 laptop has no problems at all, and if there was and just from the first time they caused me this problem id smack em in the face, however i do funnily enough have a similar story with my blackberry 9300, the trackpad on it wasnt working with my SKIN, it wouldnt move at all, i went to the 02 shop with a 10 minute old blackberry and showed the assistant who was chinese cockney, she laughed at me and showed me how smooth she could move around the menu bar on my blackberry, i said to her whats your point i grabbed the phone moved my thumb and 4 fingers each one across and showed her that it wouldnt move, she laughed at me and said whats so hard about it your only going up down and around, i warned with this "listen you slinky eyed slut if you think im a Fuykin (spell deletion) spastic then think again, i design e-learning factsheets using apple motion photoshop and final cut and logic pro, i think i know how to go up and down" she called security and kicked me out, livid i phoned up customer service immediatly and explained to the gorgeous sounding mancunian lady who was horrified i had been treated this way even after telling her what i said to the slinky eyes, she phoned the store and told them to replace my blackberry..
i proceeded to go into the store after id been called back in, brought out a bb, trackpad didnt work again but did for her, i demanded that they go through them all as i had just paid £220 for a phone that doesnt work with my SKIN, after the 4th phone, she said she would do no more, i said what you gonna do then, she said she could offer me 80% of the cost of the phone to put towards another one, i then said this " if you dont get me another blackberry that works by the time i leave this store il stick it up your arse, put my hand down your throat and pull it out" at that point an indian guy walked in and said that the bb had known issues with people who had playstation thumbs, worn out basically, he was the store manager, the equivalant of jesus, and we went through 4 more phones and low and behold the 10th blackberry, after more than 2 hours of arguing and bitching, the 10th wonder arrived it moved like pele on a football, a concorde through air, what a joy it was a working phone that i could use without having a tshirt over my thumb to move the menu, and i couldnt be more dissapointed, the worse phone i have ever gotten, next phone iphone 4s ... and i spilt coke on it a week later but still works though... (im not racist just to state i just get angry when people mock me especially when i know im right)
I disagree with those who are bashing the OP and saying he or she is being unreasonable.