That is 'normal' for a leak in the roof.

I was thinking that there was a leak too, but I can't be sure. The attic isn't on/near that part of the house, so I can't inspect the ceiling from there. There's no sign of water on the ceiling and I visually inspected the roof. I found no sign of a leak. Is there any other way to identify if there's a leak or not? Plus, if there's not a leak, what should I do to repair it? Thanks.

Two options.
I don't see the usual stain associated with a leak. However, that is the classic evidence of a leak.

That means two options:

Fix it and see if it reoccurs.

Or:

Cut out a section and look for a leak.

Water can follow rafters/joists and show up many feet from a leak.

Handymac,

I'd like to take the first option--fix it and see it if reoccurs. Could you please tell me how I could fix this?

Thanks

Cut off the loose tape. There is loose tape on both ends of that tear.

You will need a piece of paper sheetrock tape, some drywall compound, a 6" drywall knife(like a wide putty knife), and a hand sanding pad with open mesh sanding material.

Apply a thin coat of compound to the ceiling area along the seam. Apply the tape to the mudded seam and press into the mud. Then apply a thin coat of mud over the tape, keeping the coat as smooth as possible. Let dry for 24 hours and lightly sand completely smooth.

Then spread a thicker coat of mud over the entire patch area. Use a wadded up paper towel or plastic bag to try and make the wet mud splotchy like the rest of the ceiling. There will be sharp points on the peaks, don't worry about that. Once you have the area as close as possible, wait about an hour and flatten those peaks to the same level as the rest of the ceiling using the knife and pressing it lightly across the mudded area.

Then paint with ceiling white paint after 24 hours.

It looks like a section of the paper drywall tape was never properly adhered to the ceiling board, resulting in an air bubble between the tape and gypsumboard. It just finally opened up.
I'd use Handymac's procedure, making sure to cut back on the tape until I found it to be securely embedded in the mud.

I don't necessarily see any water staining.

Suppose you just get some Elmer's white glue. Put some glue in there and roll it back down with a hard roller. If it sticks you're done.

If you patch and paint, you might end up painting the whole ceiling so you can't see the new paint spot.

Yup that's a leak. Check the floor under the leak for discoloring. If you don't fix the leak it will come back and you will have wasted your money.

Nobody mentioned this, but the first thing I would do is get up on that section of the roof and see if you can eyeball something that would cause a leak. Especially on a 4-year old house that should have shingles in pretty good shape.

About 5 years after I had new shingles installed on my house I heard the dreaded "drip-drip-drip" one rainy day in a room I seldom use. An entire section of ceiling was ruined. Next day, I got out the ladder to see what was going on and I spotted the problem as soon as my eyes got above the eave: a roofing staple half-shot into the face of a shingle. Took about 10 seconds to pull it out and dab some tar on the tiny hole, and about 10 hours to replace, re-mud, re-texture and paint the ceiling.

Before I spent a lot of time fixing the ceiling, I would invest a little time inspecting the roof above the leak site to see if you can nip the problem in the bud.

And be careful up there, it looks like a steep roof...