I wonder if problems like this might not be brought on by using undue pressure on the strings, which is easy to get into the habit of doing early on?

Press the string down behind the fret only as hard as you need to to get a good, clear tone. No harder!

Two members of the Los Angeles Guitar Quartet, Scott Tennant ("Pumping Nylon") and William Kanengiser ("Effortless Classical Guitar") have excellent instruction DVDs out in which, among many other things, they address the problem of pressing the strings harder than you need to. Well worth getting, no matter what style of guitar you play. Can't help but pick up some good ideas.

Here's a simple from "Pumping Nylon:"   CLICKY.

And check on the other videos on the right side of that page. Kanengiser is there, too.

Don Firth

P. S. Both of these guys are mind-boggling when they cut loose and play. This one by Kanengiser makes me want to go out and stomp on my fingers!!   CLICKY 2.