The most likely cause is the lens aperture diaphragm moving during Live View. To maintain an accurate exposure preview, the camera may adjust the aperture as you change settings like shutter speed. On some lenses, especially third-party ones, that diaphragm movement can be more noticeable and sound unusual compared with your other lenses.

A simple check: while changing shutter speed in Live View, look at the front of the lens and see whether the aperture blades are moving. If they are, that is probably the source of the sound.

Since the banding appears only on the Live View display and not in the saved images, it is likely just a display/preview artifact in low light rather than a problem with the actual photo. Overall, this behavior sounds normal if image quality is unaffected.