PTbiker

As you can see, there's alloy missing at the seam, and something, maybe the alloy, or a pebble, or sand, got inside the rim, making a noise whenever the wheel spins. At first, I tried to get it out with a vacuum cleaner, without success, only to realize the thing(s) inside the rim's edge doesn't come near the seam. I've also checked if there's something inside the hub, but found nothing. So, what's going on? Is it possible to stop the rattling? Can that crack/hole lead to catastrophic failure?

FBinNY 

This type of rim is joined with 2 pins inside the raised shoulders. That leaves 2 hollow channels running full length less about 4" where the pins are. It's possible that the pin bumped the edge when being inserted, and drove a bit ahead, which is what you now hear.

First of all, there's nothing to worry about. The pins extend about 2" to either side of the joint and aren't going anywhere. Also, the rim is under compression when spoked so cannot ever pull open. In fact, these rims were sometimes shipped with the joint not fully closed, and it would close when built.

As for the rattle. I assume you heard it when spinning the wheel slowly, because at any speed anything inside would be driven to the outer edge and immobilized there. So, you'll never hear anything when riding, and if you do hear anything now when spinning the wheel at any speed, look elsewhere for the source.

PTbiker

Indeed, the rattle can be heard when the wheel is moved by hand, like a steering wheel, and it becomes ever more audible as the wheel slows down.

FBinNY 

My best advice is to ignore it.

If this isn't possible for you, drill a 1-2mm hole into the shoulder someplace other than near the joint or valve. Inject a small amount of grease, or a glue, shake the rim to settle whatever's rattling down so it gets stuck

Of course, it's 50/50 that you pick the correct channel, so you may have to repeat.

Then again, you could just forget about it.

grumpus

If there's debris inside the rim channel you may be able to catch it by wicking superglue into the gap at the join, and turning the rim so the whatever gets stuck in the glue. The rim is fine to use, as long as it doesn't drive you crazy..

KerryIrons

Exactly my thought. You would think that the spinning speed of the wheel would force any bits and chunks to the wall and that would be that. On top of the ambient noise of just being outside. I've had rims with bits of loose aluminum inside and never heard them when actually riding the bike.

79pmooney

I had a broken nipple top rattling inside a rim for years. A deepish velocity Aero. I'd dropped full nipples in while building (no well a al Mavic Open Pro) and hated chasing them out. Eventually I went after the nipple top and have enjoyed the silence since. (I would hear it on bumpy roads, even at speed.)

himespau 

Ride faster and you won't hear it.