They're both correct.  The only difference is that the version with 'in' is giving more information about the place.

If you say 'in there' we know that you are referring to the interior of a specific room or a building. You are emphasising the fact that you are outside that place, and you want to know what's happening inside it.

For example, you are in a corridor and you hear a lot of noise coming from inside a particular room. In that case, you might say "What's happening in there?", meaning 'inside that room'.

 You can, of course, replace 'in' with other words indicating location, such as up, down, out, or the more general over.

Here's a little exercise.  Put the right adverb of place in these sentences:

1. You're inside a room and you hear a lot of noise in the corridor. You ask: "What's happening ........... there?"

2. You're on the ground floor of a building and you hear a lot of noise from the floor above you.  You ask: "What's happening ............. there?"

3. You're upstairs and you hear a lot of noise from the floor below you.  You ask: "What's happening ............. there?"

4. You're in a big park and you hear a lot of noise from somewhere on the other side of the park.  You ask: "What's happening ............. there?"

Thank you for clarifying, Bushra.

In that example, you should say 'out there'. If you are inside a classroom or hotel room, for example, and the people making the noise are outside the room, you would say 'out there'. This shows the contrast between where you are and where they are.  You are enclosed between the four walls of a room, and you're talking about what's going on outside those four walls, so 'over there' doesn't really work in that situation.

We tend to use 'over there' to mean 'in another part of the same place', where the place is open.  This could be another part of a park, as in my example, or it could also be in the same room. For example, if you are at a party in a large room, you could point to another corner of the room and say that your friends are 'over there'.  Or 'over there' could be another part of the country or even another part of the planet. If your friend lives in Canada, for example, you could say that you want to go and visit her 'over there' ( in the part of the world where she is) or that she's going to come and visit you 'over here' (in the part of the world where you are).

I hope that makes sense.

Diana your discussion is much more helpful for me. Su.Ki. gave a interesting comment as well as exercise. I have put right adverbs, can you check them please i.e.

1) out 

2) up

3) down

4) over

But Su.Ki. I have a question that you told, we can put "over" anywhere then can we put it here in these all sentences or these are particularly made up just for other (out, down, etc) adverbs. 

Waiting for answer.