rattling noise

So something on my bike has started rattling. at first i thought it might have been my tools rattling around the seat bag but that wasn't it. i checked most of the components and everything is nice and tight, the only thing i could think of was that my chain loosened up. i put a new one on when i upgraded my components. would that cause the rattling? my last chain never did that.

thanks

Where is the rattling coming from? Does it correlate with the pedal stroke, or with road bumps? Only in certain gear combos? Could be anything from a loose component to a stretching cable => slightly-off derailleur to a bearing in the BB.

seemed to be coming from the crank or further back, originally thouhgt maybe my back wheel or cassette was loose but it wasn't

occurs mostly on pedal stroke especially on the bigger gerars in the back.

On my bike the rattling is because of the card I have clothes-pinned so the spokes brush against it as they go by. It makes my mtn bike sound just like a motorcycle. Oops, that's not the input you were looking for.

Is the back wheel loose, e.g., did you recently change the rear tube and maybe not slot the wheel back into place perfectly before tightening the clamp?

I was gonna suggest the noise was his nuts, rattling around in Steph's purse, but he hasn't been married that long, yet...

Agree w/ Bob, the wheel not being centered correctly in the dropouts is the first culprit to check.
Next, make sure the cassette lockring is tightened snugly.

Also - you could have a broken spoke, a loose or missing chainring bolt, loose seatpost clamp or head, maybe yer crank bolts aren't tight enuff.

There are lotsa things that can cause annoying noises, and they don't always sound like they are where they are - the tubes on a bike can make something like a loose saddle sound like a BB problem - believe me, I've been there.
(I had that exact above problem - coulda sworn it was something to do w/ the BB or cranks, when it turned out that all I had to do was lube the seatpost/seattube, and where the seat rails met the post head, and then it was blessed SILENCE. )

Oh, thought of another annoying potential noisemaker - loose bottle cage.
Or even if ya don't have one, maybe the hex nuts for where one could go are loose.

its more like a knock/pinging type noise rather than like a penny in ajar type rattle. i checked the back tire, cassette etc no movement.
kind of hard to explain the sound with justice.

the sound coes on teh downstroke which made me think it was the chain it isn't all the time on every peddle though.

Conventional bike wisdom says that if your chain was worn enough to need replacing, the cogs you use most may be worn enough that they no longer mesh well with the (new) chain. I haven't found this to be true, but hey, it needed to be said. If/when the chain is loose, it's more of a "grinding feel" than a rattling sound.

You can easily add about two pounds of small stones in your buddies seat post.

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Conventional bike wisdom says that if your chain was worn enough to need replacing, the cogs you use most may be worn enough that they no longer mesh well with the (new) chain. I haven't found this to be true, but hey, it needed to be said. If/when the chain is loose, it's more of a "grinding feel" than a rattling sound.

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I think it goes -- if you replace the cassette then you shold replace the chain, but the other way around isnt required, still a very good idea though.