The Cassini spacecraft took readings of the day length of Saturn – and the length of time it takes Saturn to complete each rotation. It is six minutes longer than the rotational period measured by Voyager I and Voyager 2 in 1980 and 1981. Go to http://tallbloke.wordpress.com/2014/07/29/apparent-six-minute-slowdown-i… … and then do to a post of last years, http://tallbloke.wordpress.com/2013/09/02/scientists-baffled-to-discover…
The radio sounds of Saturn's rotation are like a heartbeat and can be heard by visiting www.jpl.nasa.gov/videos/cassini/0604 and www-pw.physics.uiowa.edu/space-audio/
It is thought that the idea of a rigidly rotating magnetic field is wrong and in that way the magnetic fields of the gas giants may resemble that of the Sun. Thjis does not rotate uniformly. In other words, they don't think Saturn or Venus themselves are slowing down but the magnetic fields vary over time, perhaps in a cyclic fashion.