Grammar in「ぶいぶい言わせる」


My question is why is the causative form 言わせる used in this phrase.

I've done some checking, but I haven't found a good answer yet so I thought'd
I'd ask here. As a set phrase I know the meaning since it is used in a quite
specific context. But I don't get why 言わせる is in there. It doesn't seem to
make sense. Is it a 'forcing someone to say' 言わせる, or is it a 'letting me say'
言わせる? Or does it have nothing to do withing saying at all?




It's hard to give a definitive answer since the etymology of this phrase seems
to be fairly uncertain.

Some people believe ブイブイ represents a sound from some external object. [Some
say](https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q1443514199) it
came from the sound of a large car/motorcycle engine, the symbol of freedom
and wealth. [Some even
say](https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q1256688462)
ブイブイ is the sound made during a sexual intercourse. If one of these is true,
ブイブイ言わせる makes sense simply as "to make a motorcycle/etc sound ブイブイ".

Other people believe this ブイブイ represents something actually said by the
person themselves, whatever it may mean. In this case, ブイブイ言わせる should mean
"to allow oneself to say ブイブイ". As you already know, Japanese "causative form"
is not always forcible, and it can indicate allowance. For example you can say
キャンセルさせてください ("please allow me to cancel" rather than "please force me to
cancel") and お邪魔させてもらいました ("I received the favor of allowing me to visit").

