I am just getting into sound and am very much a novice. I recently purchased a Zoom H4n and a pair of MXL 603s. I'm attempting to record a choir I'm in using this gear. I've made some test recordings and have also recorded a rehearsal. In these recordings I'm noticing a low frequency bumping noise. At first I thought it might be the microphones picking up steps, but it happens when there are no steps and only seems to happen in one channel. It also sounds electrical to me and not caused by an external sound source. Here are a couple of audio samples that exhibit the behavior in the right channel. has some very rapid "bumps", and has a number of distinct ones. I've tried switching cables and microphones, but haven't had enough time to really track it down. Any ideas on how I can debug what's going on here? Does this problem sound familiar to anyone? Our performance is tomorrow, so I don't have a lot of hope that I'll be able to get rid of this by then. It does seem that a high pass filter in Audacity takes these out pretty well. Thanks in advance for any ideas!