Noise Cancelling malfunctioning after disassembly

Ever since I took apart my headphones (as part of the repair guides I made for these headphones on iFixit), the right earpiece's Noise Cancelling has malfunctioned.

It makes crackly sounds and a weird fluctuating pressure that kind of feels itchy, and when it gets pressurised enough in the cup, it makes a really loud, almost pulsating whistling sound. I have to use these headphones without the noise cancelling at the moment to prevent this from happening, which is a big shame.

I've reset the headphones to factory settings, which didn't fix the issue either.

I've inspected the solder joints between the NC mics and the PCBs and they seem fine (but I really don't know much about soldering and I don't have a soldering iron). I'm not that experienced in this sort of technology so I don't know what the underlying issues could be, or what I could even be looking for, really. :S