Unknow rtp codec 98 received

I have installed a beta version of asterisk and using realtime. I always get this in my CLI whenever I’m on hold.

Sep 23 14:10:47 NOTICE[686] rtp.c: Unknown RTP codec 98 received
Sep 23 14:10:47 NOTICE[686] rtp.c: Unknown RTP codec 98 received
Sep 23 14:10:47 NOTICE[686] rtp.c: Unknown RTP codec 98 received
Sep 23 14:10:47 NOTICE[686] rtp.c: Unknown RTP codec 98 received

Anybody knows what this is?