Question H80 back fan throttles in then turns off, rinse and repeat in regular intervals

[Nachmanowicz]

Yeah my outermost H80 fan throttles like crazy super fast then turns off and goes back in in regular intervals no matter what. Its really loud, no matter what setting on the button thingie on the h80 itself.
I was wondering if hmmm... a-anooo, e-etoooo I can do something about it.

 

[COLGeek]

Is it only the single fan doing this? Are you using 2 or 4 fans with the H80?

If you swap fan connections, does the problem "move"?