Originally Posted by
HillRider
I have a Mavic CXP-33 rim (double wall alloy rim) with a fragment of metal, probably from when the spoke holes were drilled or punched, that's caught between the walls and can be heard rattling at low speed. It's not audible when the bike is moving at any real speed. Several attempts to find and remove it have been unsuccessful and, after 36,000 miles, I've learned to ignore it.
This is likely the rim's joint plug that's broken loose. Many Mavic rims have this noise. Not quite the same as might be plaguing the OP but an object in the rim just the same. Some have driven self taping screws or dripped glues into these mavic rims to quiet the plugs. Andy