Same time frame for ALMA lower sideband LSB (left) and upper sideband USB (middle) and the absolute difference between the two sidebands (right). The white box depicts a relatively quiet region of the field of view. The blue crosses mark the location of five bright features analysed in here and the cross enclosed by the blue square marks the location of the feature whose transverse oscillation has been shown in Fig. 3. The blue crossed circle marks the pixel shown in Fig. 2.