"Any ideas:"

The sound is water going through a trap and a syphon. The trap may be intentional - or it may be unintentional (a dip in the pipe). The syphon indicates to me that it's got a pretty clear path and plenty of drop.

Your builder absolutely should be able to tell you where it goes. Tell him to ask the plumber who installed it.

Just for grins, put your ear up to the pipe and see if you hear anything when a toilet is flushed.

It should not be connected to the drain.

Is there a significant slope away from your house? I would follow that slope and look for a discharge. The slope would need to be something significantly more than 30" and some distance away since it takes 6 seconds to complete.

You can have it smoke tested to try to find find the other end.

Thanks for the comment. Pushed builder to help. Water dumps into larger pipe 75’ away. That pipe dumps into gutter across street about 3’ down. Have anxiety because our pump runs every few minutes 24/7. Wanted to eliminate possibility of water returning to base of wall.

Sounds like you have a lot of water around your house or a high water table.

-Make sure that the surface grade goes away from the house all around. Water should not pool near the house.

-Make sure that the downspouts empty so that water flows away from the house. It may require drain pipes. And of course, keep your gutters clean.

With such regular operation of your pump, install a back-up to cover you when the pump fails or power goes out. Otherwise, I concur with Jake

Installed Generac for electric outage. Looking at Water Comander backup for when pumps reach end of life. Comments much appreciated.