Good for you! That's the best kind of speedo issue. My '04 RMK was exactly the same!!! I re-routed the speedo cable when I replaced it - making sure there were no tight bends when the cowling was closed.
2004 Polaris Trail RMK 136
1997 Ski Doo Summit 500
2000 Arctic Cat ZL550 ESR (in NY)
2000 Arctic Cat 440 Panther (sold)
1980 Arctic Cat Jag 3000 F/C (in NY)
"If it ain't broke, take it apart and find out why!"