Why are my earbuds making dolphin noises? What I'm hearing...

Of the three vocalizations dolphins produce, my iPhone 6 earbuds have started making two: whistles and clicks. This clip is the closest I could find to the sounds I'm hearing. Now of course, these noises only approximate dolphin-y noises. The whistle sounds more electrical, the clicks more mechanical, than the organic noises of actual mammals. But they do share many aural traits with dolphin vocalizations, so it's a quick way to explain what I'm experiencing. Some of the traits held in common are pitch, note length, and note frequency. I'll visualize their amplitude over time with some rudimentary ASCII charts.

Time →
Amplitude ↑

Whistle (pitch is high):

_--````````````------________

Clicks (pitch is Mid-range):

_- _- _- _- _- _- _- _- _- _- _- _-

What I've learned so far...


These noises are noticeable when there's no other audio. I usually hear them before I make a phone call or start listening to a podcast. 
The whistles stop if I unplug my standard-issue earbuds, letting the cord dangle. The clicks pretty much stop then as well.
Jiggling the cable—whether it's plugged in to the iPhone or not—does nothing to influence the noises. I've tried jiggling the cable at all the junctures where I suspect a weak connection might form without avail.
My attempts to decipher the language of dolphins have yielded no clues into a semantic interpretation of these noises. (Okay, this last one's a joke. But my question is genuine, asked in good faith.)


What I'd like to know...

What is the explanation for this phenomenon?
It's not a driver/software/audio card issue, because the dolphin noises don't occur with other headphones or when playing music through the speaker (via Buscar above). It's probably a bad ground (via soulshined above), but without stripping the wires and testing each connection, it's impossible to say for sure.

I went to the Apple Store with a Genius Bar appointment for another issue (cracked iPhone screen) and asked them about it. Apple replaced my headphones for free.