As per @walter-i. 's recommendation. A forum search of MP3 screeching results in a lot of problems experienced in Vegas Pro but is without a resolution. Transcoding is possibly the best method to avoid the problem. And no, it is not ideal to have to do this.
I have tried several different files. Unfortunately all of them end up with the same result...
How have you transcoded the audio? Hopefully not in Vegas Pro as that is where the problem lies. Transcode by using free Audacity - others on the forum may have better recommendations.