I don't have a V:25, but sometimes I get pops if I have a ground loop ground loop somewhere. Plugging a pedalboard into a different power outlet than the amp is one potential source, as is using a single power supply (Godlyke Powerall, DC Brick, etc) to power effects both in front of the amp and in the loop.
Higher quality power supplies with buffered outputs (Pedal Power series) help to prevent that issue.