Noise from the rear wheel, tear-down help needed
 

I have a older road bike wheel for my 1986 Serotta. It's a Shimano 600 tricolor 130mm hub for cassette. It has a 8-speed cassette installed. The rim is a Mavic Open Pro that is about 25 years old.

The wheel makes a rattling sound that I want to eliminate. It is also no longer true, and I'll have a pro rebuild it with new spokes. First, I want to eliminate the source of the noise.

I've just changed the cassette, just to make sure the cassette is not the source of the noise. My current theory is that loose eyelets in the rim might be the problem. The hub seems fine, no mechanical issues in the last 500 miles.

What steps should I go through to isolate the parts of the wheel that is causing the noise?

You need to separate the various aspects that might be causing the noise from each other. Does it rattle only when riding? Only when pedaling VS coasting?

If you're considering a new rim and spokes on the old hub then before you do you should open up the hub bearings and see their condition. Are the axle cones pitted or rough? When the wheel is spinning, secured in the frame without a chain, how does the wheel feel? Place a finger on the axle end and can you sense any vibration/roughness? Then repeat but with the freehub body held still (as in how it is when coasting)?

Rattle is not the usual term used to describe a hub or freehub bearing roughness. Still if you're going to the expense and effort to relace a new rim, the hub's condition should be determined and judged as to it's worthiness. Andy.

There aren't many components of a wheel that can come loose to the point of rattling.
I suspect it's the little aluminum sleeve inside the rim at the SUP welded seam that has come loose. It's not an uncommon problem with older Mavic Open Pros. (Which weren't around 25 years ago - they're probably more like 10 years old.) You can try "gluing" the sleeve in place by squirting a bunch of watery glue (like Superglue) into the rim through the valve hole and then waiting for it to run down to the opposite side and harden, but most of the people I know who have run into this have either just ignored it (it's only noticeable when the wheel isn't rotating) or replaced the rim with a completely new one.