OK, I did the reset of Spotlight and had it re-index. No go same 16 MB/s peaks every 10 s.
I have a clone of my drive with OS X that is a few months or so old. When I start up from that I don't get this peaks, so it must be something that happened after that. I have no idea what, though.
I'm having the same issue. did you manage to fix this?
Retrieving data ...