If the blinking light on my PC case is to be believed (which supposedly indicates something being written to the hard drive) then there is almost always non-stop activity. That said, there is no indication of how much data is being read/written. I have checked and actual disk activity was nearly zero most times with just little bibs-and-bobs writing every few seconds…practically nothing.
I can believe some till manufacturer had shitty code though and the drive was being heavily used all the time. That would make a difference.