According to Roll Call, they're frustrated that House Democratic leadership has been slow on ethics reform. They recognize that if they cannot tell the voters that they did something to clean up Washington, they'll be behind the 8 ball come election day:
Frustrated that the House task force assigned to review the ethics complaint process has yet to issue an official recommendation after nearly six months, freshman Democrats are mulling the introduction of their own proposal, lawmakers said...
Nonetheless, several freshman Democratic lawmakers — many of whom campaigned on anti-corruption platforms in the fall — said they have discussed moving ahead with an independent proposal to reform the ethics process, potentially before the House begins its monthlong August recess.
“It could include a new proposal,” said one Democratic freshman who discussed the issue with other House freshmen last week and asked not to be identified...
Many freshman lawmakers had earlier endorsed a proposal by Rep. Baron Hill (D-Ind.) that called for abolishing the Committee on Standards of Official Conduct and replacing it with an independent, bipartisan commission, but it is not clear if that legislation will be up for consideration when freshmen meet to discuss an ethics proposal.
First off, you can interpret this article as a shot across the bow of leadership. The Freshmen want something done, and talking to Roll Call about it is a clear sign to the Speaker and other leaders that they take this very seriously.
Second off, if they are politically astute, they will endorse the idea of an outside, impartial ethics review body. The voters are likely to regard any ethics reform cynically, but giving authority to investigate and discipline Members to an outside body is one thing that might make a substantive difference -- particularly if such an entity was actually up and running by election day next year.