Hi Rich,
You might of already figured it out as I see this is an old thread, but i've been having the same issue with my Dapol 121 that i fitted with a Zimo MX634 chip today.
I came across your post on here long before I discovered the solution, so maybe this information will be of help to you, or anyone else with the same problem in future.
In essence it appears that it is the Back EMF functionality that is causing the noise, as it looks like it is set to be on max by default.
To adjust the Back EMF is CV 58. The default value i had is 255, which is fully on. Set this to 0 to turn the Back EMF off.
This should solve your noise problem - it did with mine.
Hope this helps.
CoBoLoco