I could do with so advice. Got new bike just before Xmas, due to work I've only been out four times but I noticed that after each ride the cassette is showing signs of surface rusting. Spoke to LBS and they said to re-lube after each ride. Have done this and it is still the same, if not a little worse. It's a Shimano CS-HG20, 9-speed, 11-34.
Not sure if I'm concerned about nothing but never had this issue on my previous bike with a SRAM drive train.
Anyone had similar issues or advice for me.