A classic symptom of a Colt action that's been tampered with is failure of the trigger to return and "push off", where the hammer can be pushed and it'll un-cock.
This is something you can't fix at home, and something almost no local gunsmith will be qualified to work on without further botching it up.
Colt will still repair the 357, so I strongly recommend returning it to them for a proper diagnosis and repair.
The 357 is a premium Colt revolver and very well worth repairs.
They'll send you an estimate before starting work.
Check the details for repairs on the web site:
http://www.coltsmfg.com/