I read in an interview that Noam left Salmon to play for John Cowan's band, as he wanted to do more traditional stuff.
I interviewed Noam a year ago and asked him about the shift from LoS to Cowan. At that time, Vince & Drew were already thinking about backing off the Salmon touring schedule and the opportunity to work with Cowan looked pretty good. But Noam thought, initially, that he'd be able to keep up with both bands. Then the scheduling got out of control and he made the jump to JCB.
In the end it seems to have worked out OK. Despite his entanglement with HTGAB and Punch Bros, Noam has still managed time for the occasional LoS reunion. I understand another solo record is also in the works.