I have been noticing ticks and pops coming from only my left speaker ... Switching the phono cables switches the noise to the other speaker. When I put on a test record and listened to a dead portion of it, a thump came on about once a second but only from the left speaker ... Could it be my cartridge ...Yes, it could. To isolate that, reverse the L and R channel connections between the cartridge output pins and the pickup arm wire. If the noise follows and is now on the right channel, then you know it's the cartridge.