If you own an old DualShock 4 controller, you might remember an issue with the triggers which could become squeaky over time. This issue was caused by the build quality of the DualShock 4 controller, just like it happened with the launch model analog stick, whose rubber used to wear off rather quickly after use.
This issue might have been fixed by Sony as the newer build of controllers use a different mechanism for the triggers compared to the old controllers. Here is an explanation given by reddit user B_Boss on this matter.
A small explanation. The newer method Sony has seemed to use to totally eliminate broken triggers and even squeaky triggers is to simply place the spring (1) onto a hinge totally separate from the pivot (2). In launch models and somewhat later, the spring was always placed onto the pivot (2) which caused squeaking and ultimately, a broken pivot since the stress and wear of having that spring constantly moving onto it caused it to break easily. Now this problem is potentially eliminated on both fronts due to no stress caused by the spring on the pivot. Awesome job Sony!
You can see the new DualShock 4 triggers in the image below.
To check out your controller triggers, you will have to see the model number on the back of the controller to determine if it contains the new triggers or the old one, as detailed by user cameronks.
There is a way to tell if you have a newer controller:
Look on the back at either the model number or the FCC ID. If it ends in an “A” that is the latest stealth revision. These have been in circulation since about late summer/fall of last year.
While it took a while for Sony to fix this issue, it is nice to know that they have improved the build quality of the newer controllers, just like they did with the analog stick for the launch model controllers.