Bicycle Mechanics - cause of forward pedaling freewheeling

My 2006 Specialized hybrid started to freewheel this A.M. just as I was leaving the house. I noticed it the last time I rode it that it was acting like it would slip a cog once in a while, the bike has a few miles on it, maybe a 1000 but not abused. I tried different gear combos but it still would do this. Any ideas appreciated. Gonna take it to my dealer and have then take a look but would like have a few clues before I do.

Your freewheel/freehub pawls are gummed up. Flush with your favourite degreaser, let drain, re-lube.
http://sheldonbrown.com/freewheels.html#lube
http://www.icebike.org/Equipment/freehub.htm

This is not a freewheel its a 9 speed cassette does that matter?

This is not a freewheel its a 9 speed cassette does that matter?

No, it's basically the same mechanism. I have freed both freewheels and freehubs (cassettes) the same way. Sometimes you can just squirt some penetrating oil or light lube past the seals and not need to take anything apart.

I'll check it out after work.

If it's rained/slush/frozen in the previous days then this will also cause problems - albeit temporary until it unfreezes. We see this quite frequenly on commuter bikes as fall turns into winter.

Got home this afternoon and took a look. Everything seemed fine. I had just installed some new Axiom panniers last week and I think the right one was interfering with the derailleur or putting pressure on it so when I took it off and rode the bike around it worked fine. I'm not gonna ride this bike till I can get in a bit longer ride around town here before I call it good. I'll ride the Volare till the weather gets wet then switch.

It's possible that the freehub has picked up enough water and muck over the three years of ownership to have gotten gummed up. If that's the case I'd be willing to bet that the hub bearings are probably also asking for some luvin as well in the form of a rebuild. While you've got the axle and bearing balls out to allow a good cleaning, inspection and re-greasing it's a simple matter to flush the freehub out with some brake cleaner aerosol. Shoot it in and spin the daylights out of it to rub away all the muck. Repeat until the cleaner drains out clear. After draining it and allowing it to fully dry relube it with a mix of mineral spirits and thick motor oil. The thinning helps it get all around inside fully to protect the bare surfaces from the brake cleaner. Flood the freehub and allow to drain and dry. This'll leave a nice thin but effective film of oil that'll resist water in the future. My oil of choice for this is the thick chainsaw bar oil sold by Home Depot. I thin it wiht mineral spirits about 2 parts spirits to 3 parts oil. This is thin enough to flood down through the narrow joint around the drive side cup but won't flow back out so much that it doesn't leave enough oil behind. It'll take a few days for the spirits inside to dry away completely but once it does your freehub will purr like a kitten...... assuming rust isn't the present issue. If the cleaning and oiling causes a grinding sound then it's likely you're in need of a new freehub. Especially if the brake cleaner came out red/brown colored.