I decided to stick with Jo Whiley, David appeared on April 8, 2009:
He talked about Planet of the Dead, the bus being crushed and reading The End of Time for the first time and having "a little cry". He also mentioned that he was enjoying Lily Allen's new album and what it was like to have Peter Davison standing in "his" TARDIS. Jo also did a bit with him where they were recommending other acting jobs he might like to do now that his stint as The Doctor was coming to an end.
At the end of the interview he reminded Jo that the last time he was there he was talking about the operation he had to repair his prolapsed disc and how intrigued she was about it all. So he brought the container that had the matter that was removed from the inside of the disc. He called likened it to "pork fat". You can listen here.