Try to imagine the following scenario. You inherit a rather old guitar made by a known guitar manufacturer in Kalamazoo somewhere in the seventies. You play the guitar on every occasion you get: at home, in band practice and on stage. Your band gains some momentum and the venues get bigger and bigger and suddenly you are being struck with a high-pitched, shrieky noise coming from your amp. The guitar was never messed with, the amp always held up just fine, what is wrong?! This scenario is somewhat romanticized because you will experience that noise much sooner, as long as a lot of volume is being used. The problem at hand is being called microphonic feedback due to a microphonic pickup. To understand what is actually going wrong, you must understand how things work according to spec.
When it comes to components, a guitar pickup is a fairly straight forward design: it’s just a coil of copper wire held in place by some material in some form or shape and a magnet. The magnet creates a magnetic field, the string will affect that magnetic field when you pluck the string and in turn the change in the magnetic field will create a current in the coil. That current runs through some wire, pots, capacitors, switches and then through a large wire to your amp to be amplified in order to make your playing audible for many more listeners than just yourself. The only parts in the guitar-amp-cabinet chain that really move, are the strings and speakers. So when everything is going just fine, nothing moves in the pickup. But when you experience that microphonic noise, it means that something is vibrating uncontrollably.
Imagine the coil of your guitar pickup as a coil of yarn. You can pack it tightly on a wooden stick, but the layers of yarn on the stick will still be able to move a little bit. That’s exactly what’s going on in a microphonic pickup. At high volume the wires will vibrate, and their vibration causes that unnerving noise! In order to eliminate the moving wires as a possible cause for noise, pickup manufacturers dip their pickups in molten wax (or any other liquid agent that will solidify rapidly and not liquefy easily). The wax penetrates the pickup and fills all the nooks and crannies. The wires are being fixed in place by the wax. They are unable to move, which eliminates the chance of the microphonic feedback.

Some manufacturers dip their pickups in wax a second time. This dip will fill the voids between the cover and the bobbins and all the other places that contain air. Some players choose to remove the wax that filled the voids of their pickups. In their opinion the wax prevents the pickup from sounding ‘natural’. Having a wax potted pickup makes the pickup and guitar feel less alive. I remove the wax of some pickups to make them feel more ‘alive’. In case you decide to modify your own pickup be sure to do that after the 21 day exchange policy expires.
So, what can you do with that old guitar of yours? You can try to wax pot the pickup yourself. The procedure is relatively easy and straight forward, but you can also choose to have someone else do it. The Custom Shop of Seymour Duncan is well equipped to wax pot pickups. You can also choose to install brand-new pickups, like the Seymour Duncan Jazz set if you want to stick to pickups close to what you had. If you go to your dealer you can order just about any pickup without wax from Seymour Duncan. Most pickups that are being produced these days are all wax potted. The people at Seymour Duncan’s tech support can handle all questions you fire upon them!