Double action trigger pull issue

[davis297]

I have a model 65 with a frame mounted firing pin.

I was dry-firing it and started noticing a slight "popping" sound as soon as I pull the trigger and the cylinder stop dips down into the frame. The initial trigger pull feels a little heavier now too. The sound isn't there when I manually thumb back the hammer.

Any idea what the problem could be? I plan on shipping it to S&W after the holidays.