There's a little blurb in one of this month's moto-mags (forget which) explaining that the line is called "antenna" tread or an antenna line.
The purpose is to give the tire a way to electrically ground itself so you don't get zapped by static electricity buildup. High-silica tread compounds can build up quite a bit of static as they roll, and one thin line of "regular" non-silica rubber in the middle of the tread is all it takes to prevent a problem.
Sometimes the line is visible, sometimes it's not. But it's not a concern at all.
And yes, tires with voids in the tread, such as most available for dual-sport bikes, make noise. And they tend to make more noise as they wear.
I recommend ear plugs. :mrgreen: The noise is entirely irrelevant to anything.
2002 Suzuki DL1000 V-Strom, Dark Metallic Space Blue
1983 Suzuki GS850G, Cosmic Blue
2005 KLR685, Aztec Red - Turd II.2, the ReReTurdening
Last edited by bwringer; 03-04-2014 at 07:29 PM.