Understanding how the brain incorporates sensory and motor information will enable better theory building on human perception and behavior. Recent empirical work suggests that sensory attenuation (SA) - the observation that self-generated sensory input is often perceived as less intense than externally generated sensory input - provides a window into predictive processing of the sensory and cognitive apparatus, and thus may allow to study the core mechanisms of human functioning. In this study, we aimed to estimate the magnitude and variability of SA in an online sample using PsychLab Online and the web experiment builder Lab.Js. Participants (N = 230) compared the volume of two consecutive tones in a two-alternative forced choice task. Perceptual processing was manipulated by motor behavior (active versus passive), identity prediction (i.e., the congruency of pre-learned cue-sound combinations; congruent versus incongruent), and a fixed sound offset (to account for effects of attentional differences between the passive and active condition, 50ms versus 0ms). Contrary to our prediction, we observed enhanced perceptual processing, instead of attenuation, for self-initiated auditory sensory input. Further, our results imply a subtle, but reliable impact of multiple factors (i.e. sound offset and according multisensory influences, stimulus volume, stimulus order) on the processing of motor and non-motor-based predictive information - and may point to according shifts in attention, leading to a perceptual bias. Finally, we discuss current challenges in running behavioral studies online and provide technical, as well as practical recommendations.