Microfilters vary hugely. Some are apparently total cr*p, as I found when helping my neighbour set up his broadband.
Also, some wifi routers (those with built-in modems, as most of them are) have problems; they generate noise on the line which can be heard in the phones. Suprising but true.
If you want a standalone ADSL modem, look on Ebay for a D-Link DSL-300G+ I have two of them and they work perfectly.