Rear hub rattle ?

Hey everyone,
On my last couple rides I've noticed a rattling/clunking noise (as if something is flying around and turning over inside the rear hub) if I start to sprint, it goes away and if I make a pace or slow down, it will start back up. I will take it apart tomorrow and see, but any ideas ?

Thanks,
-Greg

You may simply have a loose cassette where the cogs are rattling because the lockring may simply need to be tightened.

If the lockring is snug, but the cogs can be moved when you touch them with your hand, then cut a THIN washer from a milk jug bottle cap (or, equivalent) & fit it between the last cog & the lockring.

BTW. What type of rear hub are you using?

Shimano Tiagra FH4400 VIA

Loose cassette makes sense (just replaced it @ LBS about a month ago). I can see it "skipping?" slightly back and forth when I ride, but it almost sounds like some little thing is bouncing inside the hub. I dunno