I just found out they are using the exact same Velocity rims that we had trouble with earlier in our trip. When we wrote to Velocity they told us they had a defective batch of aluminum go through and they overnighted new rims out to us - but they didn't have any good rims in stock yet,so they sent more bad ones and then had to replace them again later once they got the good ones in stock.

So now I'm thinking they have four bad rims. We got our tandem of May 08, and they got theirs in October 08, so there is a very high chance that they ended up with the same defective aluminum we did. Our rims cracked down the middle, but it is certainly possible that the rims did different things.

Anyway, they are writing to both Schwalbe and Velocity to see what they can do.