Hi,
To start out, I am going to be using this thread to track my progress on my first ever real bike repair project, other than chain cleaning, tire repair, normal maintenance. I've bought and read many parts of Zinn & the Art of Road Bike Maintenance, and I just got The Bicycling Guide to Complete Bicycle Maintenance & Repair. I also went out yesterday and bought some tools, greases, a repair stand and a torque wrench (I have an Sworks carbon bike, and I know torque is important with carbon components).

So here's the problem. On my older Specialized SWorks I get a vibration in the back wheel at high speed descents but only when I am coasting. The wheels are Mavic Ksyrium SL's and the bike and wheels probably have 15,000+ miles on them. When the vibration begins I turn the cranks and it immediately goes away, only to resurface once I start coasting again. Occasionally if I have the pedals in a particular stationary spot (coasting again) the vibration has sometimes ceased or in the case of starting a descent may not appear, but the vibration appears to be getting worse. (to be clear - the vibration has occurred maybe 5 times, and it's quite disconcerting. It feels like the bike is going to come apart, although that could be my perception based on the fact that I am rolling around 40 mph and I feel like I am going to be killed any second!)

So while I was out yesterday I dropped by a very nice and reputable bike shop to look at new wheels. I ended striking up a conversation with what turned out to be the service manager who spent quite a bit of time giving me recommendations. This shop sells and services Specialized bikes, and the service manager I spoke to has personally built up many many Mavic wheels over the years, so I felt he really knew his business. Here were his recommendations...

1. Check over the bike completely for any cracks in the frame.
2. Check the wheels closely for any cracks in the rims, specifically where the nipple connects to the rim.
3. Disassemble the rear wheel and check the freehub and bearing areas for too much grease, or the evidence of grease. He told me that Mavic's require only a slight amount of mineral oil (which I bought while there) on the components, including the freewheel.
4. Check to be sure the wheel is true (which it appears to be)

So I am beginning my bike repair, and I thought I would post up about the process. I will take pictures as I progress and post what I find. This is probably an easier problem than I think it is, but since it's my first foray into real bike mechanics I want to get it right. Any comments or recommendation would be appreciated.