I didn't see an obvious place to post a question about my recent flight on Mesaba's RJ85s, so I apologize if this is the wrong spot. However, it appears as though there might be a couple of pilots for them in here.

I was really impressed with the spacious interior and the feel of the jet (it didn't feel small like other RJs), but during the climb there was a noise that really worried my wife. A few minutes after takeoff, the engines sounded like they really revved up higher and higher in pitch, and then suddenly quieted down again. They did this on both the outbound and return flights, so this is obviously some routine feature of the Avros. What causes that sound?

Thanks in advance!