Since the OB was considered froze to the rail, and never left the rail, it never re-contacted the rail.
The 'Double click' sound can be caused by the cue ball hitting the OB, which then compresses the rail, and then hit's the CB as it's coming off the rail.
To be a legal hit, one of the following has to happen.
1. After contact, a ball must be pocketed.
2. After contact, the CB must contact any rail.
3. After contact, any other ball, must contact any rail.
4. After contact, the OB that was froze to a rail must
leave the rail it is froze against, and then it can contact any rail. (Including the one it was originally in contact with, if it hits another ball that is not froze to the rail and it caroms back into the original rail.)
See:
http://www.bca-pool.com/play/tournaments/rules/rls_gen.shtml
3.38 OBJECT BALL FROZEN TO CUSHION OR CUE BALL
This rule applies to any shot where the cue ball’s first contact with a ball is with one that is frozen to a cushion or to the cue ball itself. After the cue ball makes contact with the frozen object ball, the shot must result in either:
(a) A ball being pocketed, or;
(b) The cue ball contacting a cushion, or;
(c) The frozen ball being caused to contact a cushion attached to a separate rail, or;
(d) Another object ball being caused to contact a cushion with which it was not already in contact. Failure to satisfy one of those four requirements is a foul. (Note: 14.1 and other games specify additional requirements and applications of this rule; see specific game rules.) A ball which is touching a cushion at the start of a shot and then is forced into a cushion attached to the same rail is not considered to have been driven to that cushion unless it leaves the cushion, contacts another ball, and then contacts the cushion again. An object ball is not considered frozen to a cushion unless it is examined and announced as such by either the referee or one of the players prior to that object ball being involved in a shot.