You certainly shouldn't get any noise at all from your ADSL.
There are various quality levels in microfilters, and it's not necessarily the most expensive that are the best. I had noise problems (and line-drop problems) with the first set I had. The ones I'm using at the moment came with something "BT" that I bought, and they are fine. Google may help with quality info.
I had one of those Netgear DG834 wifi/modem/routers, and after six months of constant problems (and zero customer support from the Indian call centre), I gave up and bought a Draytek instead. It cost over twice as much, but it worked flawlessly out of the box and has done ever since (apart from a brief interlude when the BT connection went down).