The moving noise/moving spur you are seeing on the ADF4159 is normal. We call it a wandering spur. It is inherent in the high-order (2^25) sigma-delta modulator. It is a spur whose offset from the carrier changes over time. Depending on what instrument you use to look at it, it appears as a spur sweeping across the screen, or as phase noise ‘breathing’ up and down. It is seen on the ADF4157, ADF4158, and ADF4159 (and similar competitor parts). It appears worst around the integer boundary frequencies. You can reduce it by using the negative bleed current (Register 3) but it is difficult to get a robust solution that works across all temperatures and frequencies.
Our most recently released discrete PLL (ADF4155) has a new architecture sigma-delta modulator which doesn’t have the wandering spur. It also has a 125 MHz maximum PFD frequency so it may worth looking at.