Last year I used to hear what sounded like a hard drive starting up, two minutes before a recording was scheduled to start, and thought I could hear it "spin down" about two minutes after a recording finished.
Now I don't hear those sounds at all. I have placed a small sensor on top of the unit, to check the temperature, and even if I carefully set both tuners on a non-bufferable channel such as music or PPV, the temp always stays high: right now the ambient temp in the room is about 78°, and the top of the 8300HD is at 102°.