I would check the cartridge mounting pins and be sure they are securely fastened to the leads. Then the wiring to the RCA jacks or if it is straight wired check beneath the bottom cover and be sure the wires are connected properly. If you have an ohmeter you can check continuity through the leads to the male jacks with that. If all the wiring is tight and clean I would suspect the cartridge and possibly try a cheap model to see if that is the situation. Or replace the stylus in your Shure. The body of the cartridge should be o'kay. The stylus could be mis-mounted in the cart.