Depending on the fill valve, if that's the problem, it may just need the filter cleaned.
The link above goes through some of the issues.
I have a 2 year old Soiree. Recently it started to fill on its own at intermittent times. I changed the set screw level multiple times (equivalent to changing "ball" height) with some improvement. I ultimately changed the flapper with no dripping for a week. Now I am back to square one. No evidence of any leakage anywhere. A plumber came and "fixed" the problem (he did not).
Anyone have a suggestion?