This is also a rare complication from mechanical ventilation e.g. PEEP for
sleep apnea.

I've had it, non-dive related.  The 'crackling', medically termed 'crepitus'
hurts like a SOB.  The sound is akin to crunching the little bubbles used
for packing material.  AFAIK, any coughing hard enough to rupture a bleb
(sort of a micro-herniation of lung tissue) is pretty hard coughing.  I
don't see how it could be caused by a little coughing while remaining
stationary on the bottom.  Usually when it happens diving, it's from
overexpansion on ascent, the air forcing itself out through whatever means
it can.

From DAN's website:

"The most common lung condition that predisposes an individual to pulmonary
barotrauma is balloon-like extensions of air sacs (known as blebs or
bullae). These sacs are believed to be caused by degradation of elastic
fibers in the lung due to inflammation. They are most frequently found in
smokers, but they can also occur in non-smokers. Because these sacs are
thin-walled, and during exhalation tend to empty their air slowly, pressure
can build up during ascent and they may rupture. Dive physicians recommend
specific testing for divers who have experienced pulmonary barotrauma before
they return to scuba diving. The evaluation may include a set of breathing
tests, a chest X-ray or computed tomography of the chest (CT or "CAT"
scan)."

http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=40

You would have to have some pathway for air to get out of where its supposed
to be and under the skin somewhere.

The usual mechanism is through an alevolar rupture, but it can also happen
through the sinus cavities.  The latter is often associated with coughing or
sneezing, especially if you try to "hold it."

--

I've never sheezed underwater. ;^)

Man, I had a bad case of bean burrito in Coz.  Coming out both ends.
Burp. Fart.  Burp.  Fart.  The burps sure tasted nasty, I'm glad I
didn't smell the farts.