Try cleaning the rim off carefully first, use meths or brake cleaner but check the brake cleaner to make sure it doesn't affect the wheels. Also check that the center pivot nuts are as tight as you can get them without locking the brake up.
If they still make a noise you will have to toe them slightly as Jimwise suggested. I used to use a big adjustable spanner with tape on it (to protect the brake) and carefully twist the bit the pads bolt onto. Be careful though, if you have Mx 1000's they are getting a bit old now and the alloy might not be as happy to be bent as they would have been when new.