Tires: tire noise, tire noise, noise generation

Question
I recently replaced all four tires on my 2007 Prius with Continental Primera A/S P185/65/R15 86T Touring Radial.  The noise I have is quite pronounced but only while driving on dark black pavement (almost glossey).  It sounds like the pavement is wet (wooshing).  The tires are quiet all other times.  The dealer said, sometimes it just happens.  Any thoughts?  Thanks.

Answer
Jack,

I hope you realize that road surface has a great deal to do with tire noise generation and that some surfaces are going to generate noise regardless of the tires.

So I think the question now is:  Was this a problem BEFORE you changed tires?