The issue with whining motors is directly linked to the operting frequency of the electronic speed control. Low frequency controls produce much more whining than high frequency controls. I do not have any experience with Minitronics that I found encouraging, ie, I do not use them anymore. Some folks say to simply put a louder sound system in the boat or operate it further from shore. I prefer a more poitive approach and use a german controller that is totally silent. They are expensive, but very reliable, I have them in seven ships and they perform flawlessly.
Most of them are LIPO compatable, but can be used with other battery sources without issues.
They can be found here: