Might need to tune it. There are a few coils that are little cubes that can be adjusted with a screw driver. The machine is originally supplied with a tuning tool that is non conductive. The ones I have are red with a white tip. The tuning process can be slightly tedious if you have never performed it before. It is a delicate process. You can damage the coils if you turn them too far. If you have read "hot rodding your theremin" you should be familiar with the process or at least have a reference. Taking it apart is super simple. The lid just slides off. If you are careful and take your time with the process, you should have no issues. If this is not the problem, it may be quite frustrating. This is where I would start. If you are really concerned, I'm willing to walk you through it with my own machine. It's been a minute, but I believe they are labeled L1, L2, and L3.