I did a detailed signal analysis of the Langrange-4 datasets with baudline and posted it to my blog. The target is the Sun-Earth L4 position at the 1420, 2008, and 3991 MHz frequencies. Found many interesting signals. Some with modulation characteristics. Several demo videos too.
http://baudline.blogspot.com/2010/11/setiquest-lagrange-4.html
Some previous discussion about the strange Lagrange-4 3991 MHz signal:
http://setiquest.org/forum/topic/weird-maybe#comment-1459
It is some sort of wideband modulated signal with a ∆1267.226 Hz spacing between tones. The 3991 MHz is further analyzed and discussed in more detail and here:
http://baudline.blogspot.com/2010/11/setiquest-lagrange-4.html#3991