吧哒 is a variant spelling of the more standard 吧嗒 (bādā). Both mean the same thing — a soft 'click / patter / smack' sound, or the act of smacking one's lips and puffing on a pipe. Often reduplicated as 吧哒吧哒 to convey ongoing or rhythmic sound.
memory
Both characters carry the 口 (mouth) radical, signaling these are 'mouth sounds'. 吧 (bā) hints at 'puff' and 哒 (dā) at 'click' — together they mimic the noise of a pipe being puffed or lips smacking.
