It sounds like your midrange voice coil is shot or there is simply some dirt interfering with the voice coil. There should be no sound (I suspect that your midrange on the other side is quiet -- if it makes the same sound, then it might not be a rubbing voice coil but simply the sound of the speaker assembly being compressed). Since the unit is less than a year old, I would contact the manufacturer/dealer you purchased them from and ask what the appropriate next steps would be.
If I were a betting person, I'd bet you would need to replace the midrange speaker (or at least the voicecoil/spider/cone assembly -- if you do this, be sure to clean the magnet gap with folded masking tape before reinserting the coil -- send me an email for more details if you have to do that). When the voicecoil rubs as it moves, it will heat up and I believe your stickiness comes from the heat buildup impact to the speaker. You may have had the problem from the onset, but it could just be getting worse with wear as the heat damages things further and the damage then causes more heat. Or, as Gregm suggests, you could have had some dc going to the speaker.
In any case, I suggest you contact the folks you bought the speaker from to see if it is under warranty or if they have suggestions specific to your speaker.
