I think you’re talking about the solenoids within the chime box. It’s likely that your transformer is located elsewhere in the home. If you know where that is, it’d be a good thing to check in order to ensure that it meets the required specifications for powering Duo Cam Doorbell, though if you were doing an upgrade from the original Wyze Video Doorbell—and if that was functioning as expected—then I imagine you’ve got adequate power output.
The hum (and other phantom sounds that some users have described) is likely because you installed Duo Cam Doorbell without the Chime Controller, as @dave27 alluded. This has been discussed pretty extensively in other topics (in addition to what @dave27 mentioned):
Those may shed some light on what you’re experiencing.
That’s what Wyze suggests in at least one of their Help Center articles, and that article even includes the installation video for the original Video Doorbell (where you’re supposed to use the fuse/jump wire to bypass the chime). Note that doing this doesn’t completely bypass the mechanical chime (you still have wires connected to terminals) and some users have reported a buzz, hum, or other unwanted sounds even using the jump wire in this fashion, so you may want to just wire the FRONT and TRANS wires together with a nut (maybe label them to note which is which, because that can be important) and truly bypass the chime until you can install a Chime Controller.
Note also that the Chime Controller is available for purchase via the app but not in Wyze’s shop on their Web site (as mentioned in the linked topics above). 
It should be, if installed correctly (which means having a Chime Controller wired into the home’s built-in chime box). In addition to that and the Wi-Fi Chime, it can also ring certain models of Wyze Cams using the “Camera as Chime” feature.
I can’t speak directly to your other questions, as I have no hands-on experience with this one. I’m happy with my Video Doorbell v2 and its actuation of my home’s mechanical chime. 