It's a classic example of a hard drive with marginal sectors in the area being used for buffereing. The clincher is the fact the problem goes away when you change channels.
The solution is simple. Download the drive manufacturer's advanced diagnosics and run a non-destructive media scan. Any marginal sectors are replaced with spare sectors. It would be a good idea to replace the drive, particularly if the problem reappears in a few months.
There's a difference between needing help, and just being plain ole' lazy.
"You cannot teach a man anything. You can only help him find it for himself." Galileo Galilei (1564-1642)
HR20-700 with 2 TB, HR22-100, HR22-100, HR22-100, HR23-100 all running 0x5cd and networked.