Do Intamin Giant Drop models (2nd gen. free fall) use pneumatics or hydraulics to release the cars from the couplings/catch cars?

When at the top of Superman Tower of Power at Six Flags St. Louis, in cars 5 or 6, you can hear the other cars being released. It sounds like "clunk dshhhhhh". Is there some sort of pneumatic/hydraulic thing that unlatches the cars?

This sound is not heard on most other Giant Drops, due to the fact that they usually drop the cars all at once, whereas on S:TOP, they are dropped at different times.

I would think that it is pneumatic canisters that are somewhat similar to those that Intamin has used more recently for retractable brake fins on cable launch tracks.

I've noticed the cars not being synchronized on Giant Drop at Great America, so it would make sense that they are triggered at the same time but each release is delayed differently due to the wear and tear of the pneumatic or possibly hydraulic containers.