Grinch

Well its normally clutch adjustment that causes the drag, with the clutch leaver in, the bike tries to move forward when its in first. The SV does it if you put the wrong oil in, as it doesn't like fully synthetic.
Most of the time its due to the worm drive not being greased, or adjusted, then from the lack of greasing the bearings break down and it just gets worse and worse.
The other are contributing factors, but you do need to keep a eye on that worm drive.