I thought of one more thing that possibly could be causing the noise.  I installed a cutlass bearing once that was a bit on the tight side,  apparently a manufacturing issue.  The Cutlass bearing made what I would call a “chirping” noise for while as it wore in.  Might be worth spinning the prop before you launch and listen for noise from the new cutlass bearing.

   Best of luck in solving the mystery squeak,  let us know what it turned out to be. 

Best,

James

SV Sueno

Maramu #220