Most dictionaries (ABC/A Chinese-English Dict) claim that 噗/扑 are variants of each other, while giving 扑 as the simplified form of 撲.
Liang'an seems to say that 扑 is the simplified version of 噗. [This seems wrong].
Hanyu Da Cidian offers another alternative: 噗嗵.
百度知道 has the following question: 扑通与噗通的区别
With the best answer having been chosen as:
Another answer claimed:
and lastly another reply:
I'm not sure where the claims that 扑通 is not onomatopoeia are coming from, as it seems to be widely accepted that it indeed is.
- Can Anyone Clarify Things A Bit: What's The Difference Between 噗通 and 扑通?