U.S. mortgage rates dropped even lower in the week ending May 31, with the 30-year rate falling to 3.75 percent, mortgage financier Freddie Mac said Thursday.

The 30-year rate has hit a new low for five straight weeks, while the 15-year fixed-rate mortgage fell to 2.97 percent. The impact on the housing market, however, is expected to be minimal, as many buyers are having trouble obtaining financing due to tougher underwriting standards.

Compared to a year ago, rates on 30-year fixed mortgage rates are almost 0.9 percentage points lower, which translates into nearly $1,200 less in annual payments on a $200,000 loan, said Frank Nothaft, chief economist of Freddie Mac.