I can commiserate, but unfortunately I do not have a solution, I offer my recent experience in support of the “your not going crazy” category .
I was helping move a vessel this past fall, we worked on the two VF heads. My bunk was right over the fwrd pump and it was cycling every 15 to 20 min. We changed wire connections, rings, baffles, pump arms and cleaned everything. The noise
reduced and it did get to a 90 min cycle but we could not get it to operate as designed. We ended up putting a switch with the VF light panel because the constant cycling was waisting water and energy, and I was loosing sleep with the constant cycling.
This being my only experience with VF system and reading your post as a second source supports my gut that a VF will not be an up grade in my future.
Cheers and good luck
PS: I have 3 heads, a “not so quiet flush” Jabsco electric
I run with freshwater, a Jab, manual freshwater and a dormant Jab, salt water
“off shore” head
. Not a single
issue in 7+ years.