The scorpion is very sensitive and can respond to the salt in your hand and fingers when the sens is set at the prefered setting.
Tapping the coil can produce noises that come from movement between the coil and the coil cable where it enters the coil, it is able to detect the coil cable no probs at all if there is any sort of a loop or bend in the cable at that point, there will be because you have to leave some slack to allow the cable to flex if the coil tilts.
You can check for elec interference by holding the detector horizontal with the coil out in front and vertical to the stem, with detector 4 or 5 foot of the ground and at least 10 feet from any metal, then sweep the coil through 360 degrees in a large circle and listen for any changes in the random noises; if they are loudest in one particular direction then you have elec interference in which case you will have to lower the sensitivity setting or move to another area free of interference.
If it is sounding off very loud then there may be a problem in the coil (try another coil if possible)
If the sounds are loud and random then make sure you are away from electrical interference..... Also check all of the battery contacts and wires for bad contact. Moving the coil cable with your fingers where it enters the coil housing will normally cause some sound that should be smooth as you move the cable; If it is sudden and chattery then there may be a bad screen or wire in the cable; Squeeze the coil cable all the way along from the coil to the control box and listen for any sudden noises that might indicate a bad wire in the cable. Check that the coil plug is tight at the control box; Check the male and female pins in the plug and socket for tightness and straightness.
If all else fails to solve the problem then you could suddenly and severely, wrap her around a tree....That usually will quieten most detectors rather well.