I will investigate changing the reference.
The VCO is a 10-12 GHz model.
I am using the divide by 4 output to feed back to the PLL, approximately 2.5 GHz.
Will try manually programming the PLL to sit at the particular frequencies without sweeping. From memory, it works fine.
I have tried varying the CLK1/CLK2 values and they did have an effect, but I will do it again and document it properly.
Thanks！
Br,
Wayne