Nugget finding coil wont work.

G'day Guys.
Went for a swinger the other night with a mate, While looking for small bits of gold thought i would try my Nugget Tech coil on my 4500. Had nothing but noise all night... tryed a few different settings, My mate have a 5000 and a small nugget finder and it was very quite, i know the 5000 to the 4500 is quieter.
But i just wondering if anyone knows if these coils are compatable with the 4500 or of any settings to try??