No, I think it may be a hardware issue. On my previous device, an HTC One X, I had issues with the mic. During calls, the only way I could get people to hear me during calls was to put it on speakerphone. The mic did NOT work in Instagram, Snapchat, Vine, etc. It would record but there was no sound. But, it DID in fact work when recording regular videos using the native camera app. I thought this was odd and did some research. Turns out the noise cancellation mic only comes on during speakerphone & recording videos (apparently only with HTC's camera) and that is what was recording the audio during calls. The main mic was indeed broken and did not work. So only apps that used the second noise cancellation mic would record sound.
My guess is the Nexus 5 is having issues with it's two mics simultaneously recording, or maybe even just one is defective. That would definitely cause issues with static in recordings. It would also explain why some apps may have loads of static but others are crystal clear, because they use different mics.