A bad contact between the search coil and the detector electronics could be a huge problem, leading to ghost signals and reduced performance of your detector.
In this video a Golden Mask stuff explains how to fix this. The video example is with a Golden mask coil, but the same could be applied to all brands using similar jacks.
WARNING! Note the warning about using contact sprays or other liquids – this is absolutely not to be done, since liquids always make things worse and could make irreversible damages on your coil jack.