Thank you for your response. I use the earbuds on three different devices: primarily to listen to my iPod, a fifth generation, classic; then on my computer speakers (cheapy Altec Lansing's) and an even more cheapy Coby radio.
Don't know the earbud brands---got them at WalMart, but not inexpensive. Thinking the clicker was some kind of volume control, I clicked it a few times; and when nothing happened I just clicked it absent-mindedly from then on. Then all of a sudden, the sound on the earbud for the left ear went dead. Since that's the line that has the clicker I wondered if my fiddling had a delayed action.
Anyway, I eventually replaced the earbuds. The new ones have worked fine, for several months on all three devices, just as the first set did. Then, again all of a sudden, nothing---and, again, on the left side.
So I can't help thinking there's some connection with that darned clicker which, I've been told now, actually has something to do with advancing the songs one plays? If so, I need to get buds without the clicker it they still make them.