Disclaimer: I'm a newbie, my BC29 is 3 months old. My opinion should be taken with a grain of salt.
My MP20 just turned 1 week old (break-in period). Motor can be heard if you put your ear near it. If 20" NEP is on, you will never hear the Vortech. Pretty solid build from what I can tell. Customer Service is top notch from what I've read from other people's report. Mine replaced 2 Koralia 1 in a BC29. Reef crest mode is random flow which, as far as I can tell, the corals love it.
my opnion is vortech over tunze because of the built in controlling options. i dont hear my vortech running because i have a blizzard fan running over my sump when it gets too hwarm so i guess that is the only humming noise i hear. if i were you i would get the mp40 instead of mp20. IMO the mp20 works well on tanks less than 36" long. i have a mp4o on my 40 breeder and have it at time up to 60-75% power
it only makes a humming in short pulse mode. guess it only happens if there is constant starting then stopping. if i run my mp40 full blast on a 40 gallon tank you will hear the humming . IMO it depens on how hard you run it and tank size, guess it has to to with vibrations?