Coverdell ESA Certificates

I put aside $2000 a year into an ESA (Education Savings Account) for each of my kids. I can use the money to buy certificates (IRAs) up to 7 years. When I started this last year, the 7 year certificates had an interest rate of 3.5%. They've since gone down to 2.75%, and I've been hesitant to tie up my money for so long at such a low rate. Does anyone know what determines the interest yields on these types of certificates, and if we can expect to see them rise any time soon?

My credit union always adjusts their rates on the first of the month. For some reason, last week, they dropped the rates on the 7 year certificate from 2.40% to 2.00%. Was it the FED's announcement of QE3? Not sure, but I know one thing - I won't be tying up any more of my money at 2% for 7 years. I can get that with the G fund.