Go to a reputable motorcycle shop that can do suspension set-ups (unless you want to learn to do it yourself, with the help of a friend). I would go to a shop, and watch and learn how they do it.
It could be a number of things... sag, springs, rebound, compression... even pre-load.
I had the same problem with my bike when I ran the front straight at TWS. I have an Ohlins HRCS Rear, with RaceTech internals up front. I knew it was suspension, and the rear was probably too soft vs. the front. I brought it in immediately, and went straight to the suspension guys. I paid $30 to have them tweak it out. Got back on the track, and all was great!
IMO, the best place to do this is at the track, because you can set it up, get on the track to safely test it out, then bring it back to tweak it till it's perfect. I had already had my suspension set-up prior, but apparantly it need a little more tweaking to get it right.