2001 Other Chevrolet Models not starting

G30 cutaway van
The truck makes a single slick noise when tuning the key, not click, click click like a loose conection. Thats it. But if I rock the truck while in park, something must move, as it will start right up.
This does not happen all the time when starting. Sometimes it starts right up. It used to happen 1 in 100, than 1in 50, now it seems like it happens1 in5-6 times.
Thank for whatever insight you can provide.
BillT