Your engine will sound different depending on how much trim you have and whether the prop is ventilating or cavitating. Once you get used to it you can actually use this to trim the boat for optimum performance as well as looking at your trim guage and / or speedo. When I had a DS21 like yours albeit with 150hp I found it very sensitive to trim. In flatter conditions I would trim out as far as I could go before losing speed. I could definately hear a change in engine note at this stage (I think cos the prop was ventilating?). In head seas I would trim right in - the DS21 has very wide hull and you really do want to land on the Deep V part for comfort!