I have a TiVo Series 5. The system is about thirty months old. For some time now, I have recorded programs which I also watched while it was recording. There were no issues in the original transmission, but during replay of these recordings, the audio and video breaks up about every five to ten seconds in different areas of the picture and the sound breaks up by skipping and being jerky and in other ways. This is happening during many, but not all recordings. What causes this and how can I fix it? Thanks.