Sudden jarring

Bum Chain, or chain suck, Derailuer adjustment to list a few. Wheel by your local shop,preferably where you bought the bike and ask them to check it out. Is it new? if so they should fix it for nothing, probably your derailure cables breaking in. This is a good reason to never buy a bike over the internet or from a big box store.

Good luck,
Slimmer than average

I remember your recent post about a crash. Did you have your bike checked over since? If not you may have a bent dérailleur hanger or a stuck link in your chain. I would definitely have your drive train looked at, we all know how annoying a messed up drive train could be.

I had it checked over since the crash and it came back clean. But now that I think about it, I remember looking at the chain and seeing something out of place back when I first got it. It looked like something was off with a link. I'll take it back and have a closer look at it.
Thanks for the memory tap!

well if that wasn't the problem then it could be that the hanger is sticking because it needs some lube or one of the crank chain cog thingys is bent
and the last problem i can think of is your foward dérailleur is in a tottaly difrent range then the back.for example your in the front is in the lowest power cog but the back is in one of the smaller more power requiered cogs
hope you kinda under stood what i meant and if so hope i helped lol

mountain biking is to earth as diving is to water