I have had my Series 4 Tivo for about 4 months now.
For the past month or so when watching a recorded show it will get into a series of stutters. Meaning it will stutter for a few secs. then is fine for about 15 secs then does it again and will do this for a couple of mins at a time.
Now the weird part is.... I can rewind and repeat the same scenes and it won't stutter at the same time as before so I wouldn't think it is the Hard Drive.
This is happening on at least 3 different channels.