Its the same thing as an "unreviewed Android App", which is to say a completely unknown entity.
So in the YC process, folks compete to be selected and then they work to make sure they are ready on demo day. Investors know that Paul and his partners have spent many weeks with these people helping them achieve the maximum potential possible. That is a form of validating their authenticity or 'vetting'.
However, with the general ban lifted, startups will now appear "out of the blue" because they used some funding to 'reach out' to "you" a person they bought from a list (typically the HNWI list [1]). That is the noise part. If you're currently getting postal mail (or spam email) from folks who are congratulating you on your success and offering to help (personal wealth management, car dealers for high end cars, high end credit cards) then you are on that list (whether or not you think you should be :-)
Because of that, in my 'bad' scenario of how this could be a not good thing, I expect that we'll see lots of "next big thing" pitches showing up on the nightly news (it scores well in the HNWI demographic) and tucked in with those platinum card offers. What is worse, we'll see the rise of companies that prey on individuals who think they have a great idea but just can't get it off the ground. They will offer to "get them funded" by putting them in touch with hundreds of "angels." And they will just be high pressure sales guys who sell lots to unbuilt housing developments in Utah or time share condos in vacation spots. So the real opportunities get lost in all the noise.
However, I recognize I'm somewhat cynical here and this could be a really good thing. I'd like it to be a good thing because there are ideas that don't get funded today that should (or would do well if they were). But watching Shark Tank now and then you are reminded there are a lot of people who want to change the world and don't have the benefit of an incubator's advice or tutoring. Those folks are going to be victimized here.
[1] The High Net Worth Individuals or HNWI list is sold in various forms by meta-data collection agencies which identify such individuals through public records (vehicle registrations), web purchasing tracking, and other social "cues".