hi..... after two weeks or so of having arranged my brake sqeal (Avid Arch Rival 5's gripping on MavicX512's) i've got this misterious thud on every revolution of the rear wheel. It does not happen unless I brake hard on a downhill at around 30KM or over, so I cannot locate the exact position where the thud is. I examined the rim thoroughly - no defects - I cleaned it but still.
If it hapens once every time it rotates then most likely on the seam. It may be off by a little. Sadly see this often. Mavic rims are not the best things out there as many may think. Check the seam out for that.
I had a similar problem back in '95 when I had gotten a pair of the Mavic 217s on my new kona kula. The shop called mavic and they replaced the rims after receiving my old ones. My LBS ate the expense of rebuilding my wheels. It wasn't their fault. I think Kona should have caught the problem before they shipped the damaged rims out. They refused to help with the process at all.