RE: Ultimate Biplane horrible sqeel from Brushless motor
Jas,
This problem is sometimes seen on brushless ESCs when the voltage is just a bit too high for maintaining a proper sync between the ESC and motor. Typically, it happens on a fully charged battery pack when the cell count is at the maximum rating of the ESC.
The simple fix is to use less full throttle at the start of your flight. After a minute or so, it should no longer happen at full throttle. The more complicated fix is to try a different ESC or lower your cell count and adjust the prop size accordingly.
Newer ESC designs like the Jeti Advance PLUS rarely exhibit this problem. On my older setups that occasionally show this sync issue, I have learned to take-off with less than full power and fly around the field once before going freestyle.
Good luck!