help - hot rod combination pups

[hinchey1]

I recently replaced the pups on my cort m600 with a jazz / jb combination
I wired them as per instructions and whilst they seem to work o.k
there is a hum coming from the jazz at high volume.
The jb is fine I can even hold it up to a computer screen and no hum.
I have checked continuity on the jazz and its ok - even the coil tap works , but there is still that annoying hum.
Does anyone have any ideas ?
Is the pickup faulty ?

Thanks Tony