Help: Luke 3 HSS humming noise

I found issue with humming noise on my L3, especially on the neck pup with high gain setting. On the mid pup also audible but not as much like on the neck. In the between position of the pups also. As soon touching any metal part, all goes except, at the neck joint plate. Here getting even louder when I touch it. Weird..
I looked into the cavity on the back, nothing really found which can make this noise, no wires loose etc. Tried different guitar leads, no help.
Any advice/help/experience with similar issue?

Thanks,