@foliver I'm having the same problem - W.Lav Pro with my Lectro UM190b sounds beautiful. With my UM400a it's got a loud hiss.
Best guess I've got so far from poking around online is I might need to use a different microdot to TA5F adapter, but I'm not sure about that.
Sorry I can't offer more help. If you've figured this out, please let me know!