My question is how do I secure those connections and prevent this from happening? I think it occurs because I move around a bit. Do I have to stand still? I don't know if I can abide by that. I don't need to dance but want to feel free to move around without worrying about my cables feeding back.
Welcome to stealth recording! A significant practical aspect of self-worn recording setups is minimizing noise from clothing, cables, and connections. You
can do things that will allow you to move around without creating distracting noise on the recording. That said, there will also be times when something is not just right and you'll find you need to choose between standing still to make a good recording verses saying fuck it and just enjoying the music. Unfortunately the only ways to know something is not quite right is by either rigging up beforehand and plugging in some headphones to listening for noise or other problems while moving around, or by noticing a problem while recording from looking at the visual meters. And in that second case noise problems are likely to go unnoticed unless egregious.
What to do:
First make sure your connections are clean and tight fitting. Clean all connection contacts with 90% isopropyl alcohol or some kind of electrical contact cleaner. With them wet with solvent, plug-unplug a bunch of times and wiggle turn them all around. This is often the first thing that goes wrong and is easy to fix.
If the connections are mini-plug/mini-jack TRS, gaff tape them to prevent them from partly or fully disconnecting. The biggest problem with TRS connections is that most of them are non-locking. Gaff taping them together substitutes for locking. After dealing with this for years I converted all my stealth connections from mini-plug to locking mini-xlr except the mini-jacks of recorder itself because they are positive locking and much easier to deal with. I still gaff tape those connections to the recorder. Threaded mini-jack is an alternately locking method, but both sides need to have the mating threads.
Make efforts to minimize fabric noise around the microphones, and to minimize solid-born noise transmitted through the mic cable. When actively listening for noise or other problems with headphones, move around to find the limits of how much movement you can get away with before you notice noise. Maybe put a loop of cable near the microphone to reduce direct tugging being transmitted through the cable to the microphone as you move. The other things in this list tend to be more about them working correctly or not in a binary way, but this part is always variable and defines the creative art of stealthing. As long as everything else is working correctly, this will be biggest variable over which you have control that effects how wildly you can move around without creating noise.
Make sure the cables and soldered termination connections are sound and free of intermittency. Worn cables tend to suffer from more wear abuse than larger open-recording cables and require re-soldering, reworking, or replacement more often. If your gear is new this is unlike to be a problem now, but will be sometime in the future.
Other considerations:
How loud the music is effects strongly effects the audibility of much of this. You can move around a lot more and get away with other noise problems when the music is loud verses very quiet acoustic music where you will need to remain more still. But even with the quietest stuff you can set things up to allow movement without being statute like.
Other than noise, your own movement can effect stereo image, and some setups will be more susceptible to this than others. Your setup is less susceptible to this than other common methods.