One question that I am always confronted with especially after doing a mod is that the detector seems noisier. One of the major causes of this has generally been the toroid inside the detector on the coil leads from the coil socket. The toroid is set by Minelabs when they manufacture the detector but unless they fastened the toroid it can slip up and down on the wires. The toroid stops (or limits) electrical interference from the coil. It is also dependent on being in the proper position on the wires to do this. Below is a photo of the toroid and it can also be orange in color.
As you can see this one has nothing holding it and it can move freely on its own!!
Also ignore the other wires in this picture as they are mods. The standard detector has only 3 wires;
Black, Red and Yellow
Here is a step by step procedure that we have found effective:
Firstly turn the detector off and unscrew the front plate (coil side obviously). gently pull it away from the detector and locate the toroid on the back of the plate at the top behind the coil plug. It can either be held in place with silicone or cable ties. If the latter cut them off (CAREFULLY) move the torid towards the inside or down the cables towards the PCB. If on a 2000 you need to put the plate back on and use at least one scrw to hold in place, on a 2100 just push the plastic front back in until closed no need for screws. Turn on the detector and see if this has eliminated the noise if not repeat the procedure moving the toroid in either direction (up or down) until the detector is running with the least noise.
That's all there is to it. Most of the time this will eliminate most noise, hopefully. Remember this is just a tip and not the only cause of noisey detectors. We have found in 90% of cases it fixes the problem. One thing I forgot to mention is that this should be done in the field and not where you have any electrical interference (ie: near powerlines). I cannot do it here at my workshop due to too much electrical noise. So it is up to you the owner to do it. Of course you could always send it to Minelabs...
Hope this helps and happy hunting...