Good stuff. The timeline is really key to understanding this case. And if you want to listen to the recordings again, the Wikipedia article on Trayvon Martin has them.
The start time of call with Trayvon's girlfriend is only known the the nearest minute. We don't know if T-Mobile dropped the seconds or rounded to the nearest second to determine that time. The four minute call length has the same problem. But if his girlfriends description was accurate, it ended before the screaming started. And that would have been at least 15 seconds before the first 911 call. (It takes time for people to recognize a problem, call 911 and get an answer).
As for the clicking noises, to me they sound like GZ is running across gravel. Perhaps between the condo driveways or in the gap between buildings.
I downloaded everything but it's good to have a link for those who don't have access. Thanks for the Wiki article reminder!
The times are not exact - that's why I have not converted the times I noted from my audio program to military - I'm not sure how close I am with where things line up. There's the problem that T-Mobile rounds off the minutes for the girlfriend's call. And the 911 calls are only to the round minute in the transcripts I have, so I'm not sure how exact the time for the gunshot is.
The clicking noise is pretty metallic sounding to me. And it is always three clicks. There are four repeats of the three clicks. When I posted the audio file earlier some thought it was computer keys, maybe the operator was hitting the return or tab key three times to change lines.