I also found a bit of grit in one of the bearings when I was building mine, rcbearing.co.uk made up a full bearing kit for me which all seem to fit perfectly and he now has the kit for sale. Once you've run it another good check is to unscrew the inner ball studs and check all wheel bearings are nice and smooth. CVD pins can snag and new bearings may, like mine, be faulty.
The best setup I've found so far is this one, post number 8.
http://www.rctech.net/forum/electric...-services.html
with some added weight.