I use an Hitachi M12VC and I've had to replace the speed controller on one. I have a two, I keep one as a spare.
I don't recall there being any noise such as you describe from either of my routers.
Does it make the same noise as you adjust the speed controller?
Also, head over to
Collets, Nuts and Toolholders
and upgrade to their precise collets. Its been a fantastic use of my money to use my Hitachi and 1/64 bits! Yes, 1/64 bits.
I do like my Hitachi router!