This is a well documented issue here. I had the same problem many years ago. The thread is.
funkgod posted his solution on the thread. I have pasted it below to save reading through it. The solution to adjust the PUP poles. It work for me and i have never looked back. Good luck.
I have had 3 stingrays all with the same problem,
as artisan has said the two middle poles A and D are taller, so you cant tilt the pick up to the G string as it just makes the D louder.
NOT only this but if you look at the pick up from above you will see the G string is not in the middle of the pole it misses centre by a quarter so its only a quarter over the pole piece, so its not getting the middle of the field.
but reg the pole height there is a cure !! on the E.B. stingrays if you want to chance it....
take the pick up out you can leave it connected
THE 4 middle poles WILL push down, the 4 outside ones WONT push up because of the coil tensions at the ends, the middle ones will do it slow then when you put it back you can raise the pick up. JOB DONE
And remember you heared it here first folks, (or mabe not)
the main problem is the pick up is too large for the string spacing.