high pitched engine noise on 05

Have had 2005 stratus for about 3 weeks. I live in town and rarely get it on the interstates. Today, drove it out the interstate about 10 miles for shopping. Here's the problem: when I accelerate to 71 mph, a loud high pitched noise starts. Once I get to 75 mph, the noise stops. (yes I drive fast) Any ideas on what this might be caused by? Anyone else had this happen?