I have had to go through mm-wave scanners in MIA and MCO. I am sure I could have opted out if I were willing to go through the process of explaining things to the TSA employee instead of just rushing through.
I am in both because I enrolled in TSA Pre and then about a year later needed to be in Global Entry due to a sharp increase in international travel. Once my TSA Pre expires, I don't expect to have both. Right now, various frequent flyer programs still have my TSA Pre number entered and I just leave it alone.
Unless things have changed in the past several years, you should be able to opt out of the mm-wave scanner for a pat down instead. Although I guess you could do this without pre-check/GE. It just takes more time.
Between the two, I have managed to never walk through a mm-wave scanner.
As an aside, why are you in precheck if you have GE? GE gives you everything precheck has