The recent rapid rise in interest rates has some market participants talking about margin calls on MBS investors, but so far all the chatter appears to be speculative although there still could be red ink out there, somewhere. At press time, the yield on the benchmark 10-year Treasury had stabilized at 2.54 percent. In mid-May the rate was 1.70 percent. Thats a run-up of 84 basis points. One secondary market official told...