Mine used to do the same thing too. It used to make a crackling double-clicking sound almost like it was broken, but I found a DIY solution myself, which stopped it from being loose and the crackling feeling/sound. If you are going to attempt this yourself please note that this may void your warranty but if done properly you can probably get away with voiding your warranty.
NOTE: I AM NOT HELD RESPONSIBLE TO ANY DAMAGES THAT MAY BE CAUSED TO YOUR PHONE INCLUDING VOIDING OF WARRANTIES, THIS IS JUST FOR EDUCATIONAL PURPOSES ONLY, DO IT AT YOUR OWN RISK! I HAVE DAMAGED MY LCD SCREEN AND FRONT CAMERA DOING THIS, IF THIS DOES HAPPENS TO YOU, YOU CAN GET AFFORDABLE OEM IPHONE PARTS FROM ETRADE SUPPLY. http://www.etradesupply.com/ THEY SELL CHEAP ORIGINAL MANUFACTURER PARTS. EBAY SELLS FAKE PARTS EVEN IF LISTED AS OEM.
This Is What I Did:
- First off, I turned off my iPhone, unscrewed the pentalobe screws at the bottom, then I opened my iPhones 5s's screen, I used a cheap iPhone repair kit from eBay, this is required since you will need a small pentalobe screw driver, which many people don't have, here's a good tutorial on how to open the screen: https://www.youtube.com/watch?v=BMZ4tyq6OcE (Please be aware that there is a cable attached from the touch ID sensor to the motherboard, so please be super careful when opening! The touch ID is only half-replaceable, you loose the touch ID function when you replace the original touch ID sensor but still get the pressing function. This is due to Apple's strict security implementation, every touch ID sensor is unique.)
- Once I've opened it, I used a tool to remove the cable of the home button, then proceeded to the top right corner of the iPhone's body to detach 3 more cables (front cam & sensors, digitizer, LCD) I took out the screen and unscrewed the screws to the home button's metal bracket.
- I folded a small piece of aluminium foil and glued it under the home button metal bracket (The aluminum foil was thick enough to fill the space between the home button's tactic button which is the thing that allows the touch ID sensor to click/press) to the metal holder. (This was why the iPhone 5s's button was loose, the bracket didn't really touch the tactic button and therefore the home button would rub against the metal bracket when slightly pressed.)
- I screwed the metal holder back into place, connected all the 4 ribbon cables, turned the phone on & checked if the phone was still working then I closed the screen which locked into place then screwed the screws on the bottom of the phone near the lightning port. I pressed the home button and it was the best feeling/sound I've ever felt/heard in a long time, I knew I have finally fixed the problem.
DISCLAIMERS:
I am not an IT technician or expert on repairing/modifying iPhone's. I've learnt pretty much from experience and research from the internet (etc; experience from other users).
This solution does not affect the phone's physical appearance in any way, since the work is done inside, where it's hidden.
This solution might make your iPhone's home button click slightly louder, but I gladly preferred this to the old annoying double-clicking sound/feel though. If you dislike loud clicking noises try using a slightly softer material as apposed to aluminium foil and see if that works.
It is not the touch ID sensor nor the sapphire crystal glass that causes the problem, in my experience I found it to be the metal bracket holding the sensor, it is too loose and therefore it makes the home button make a double-clicking sound/feel.
As a number of people have mentioned, it is an adhesive/glue problem but in my own experience, it had nothing to do with the glues or adhesives.
If you use this solution and send your phone to Apple for warranty, they may reject it, so please remove the aluminum foil piece before sending it. I recommend using UHU power glue since it is a clear & strong adhesive but can easily be removed since it has rubber like properties. Normal paper glue should work but it may take longer to stick.
I think you can get away from voiding your iPhone's warranty as long as you don't damage the internals of your phone and leave fingerprint marks or other hints.
Do not open the screen back more than 90 degrees, exceeding this may result in permanent damage to the LCD, digitizer & sensors/front camera cable. Also do not force the screen to open, this has caused my LCD & front cam to get permanently damaged.
Do not make the aluminum foil piece too thick as this may hinder the home buttons ability to click/function properly, make it the right thickness, try and experiment which click is for you.
When unscrewing the LCD, front cam/sensors ribbon shield, please remember to put the screws back in the same screw holes, failure to do this may result in permanent damage to the logic board which in turn may give you a blue screen of death boot loop or other errors, if this ever happens, immediately power off your phone and unscrew all the holes. Then power on your phone again to see if the problem disappears, if not, you may have damaged your logic board. This has almost happened to me but fortunately, I was lucky, thank god.
You might risk damaging other parts of your iPhone when using this solution, but if you are extremely careful, the risk is pretty low.
You also risk scratch/denting your phone when using this solution, but if done correctly, this should not happen.