Audio works randomly in calls

Hello!,

weird problem occured to me. Can anyone help me figure it out please?

I am running Asterisk 11 on raspberry pi. I have configured Asterisk through LDAP and I can register, I am able to make calls too, but there is no sound. Sometimes the sound works, mostly it does not. It is purely random.

It behaves really odd, when I make a call the sound works for 5 seconds and then it stops working and there is only silence. Sometimes oposite way, that the sound is not working at all and after 3 minutes of silence the sound started working. This is really rare, most of the time there is no sound at all.

I am making the calls on LAN, Im not making any external calls.

Debug says this, not sure if this is the real problem:
[Apr 9 16:33:45] WARNING[9115][C-00000007]: res_rtp_asterisk.c:4148 ast_rtp_read: RTP Read too short
[Apr 9 16:33:45] WARNING[9115][C-00000007]: res_rtp_asterisk.c:4148 ast_rtp_read: RTP Read too short

There are another problems in debug with asterisk trying to modify ldap attribute, but I dont think this is the core of the problem.

Could anyone help me please? If you need more information, I will gladly give it to you.

EDIT:

Some update, even wierder.

I tried install Android SIP Client to my and friends phone. Calls are functional, not even a glitch. After that, I installed different PC Clients on my laptop and PC to try. No sound. After that I called from Android device to my laptop and it works like a charm again.

So:

PC > PC - silence
Android > Android - works
Android > PC - works

Anyone can solve this mystery?