The motor speed taps are used for setting speed but the real questions remain unanswered. You didn't say whether you're heating or cooling and if heating is it by heat pump or hydro-air? Minimum airflow requirements are generally needed for the equipment side of things, particularly heat pumps and air conditioners and yes, you could do damage if the speed is set too low.
The noises you're hearing are the result, as you've already deduced, of high airflow/velocity. Changing blower speeds can have many varied results, among them changing the actual static pressure of the system. This could lead to actually moving MORE air with a slower blower, something that is counter intuitive but is related to aerodynamics. Lower speed, much less resistance to airflow = more gross airflow.
If you were my client, the first thing I'd need to do is a load analysis to find out if the equipment is properly sized. If yes, then we would proceed to static pressure testing in conjunction with a comparison of a proper Manual 'D' design against what you have in your home. Likewise, Manual 'T' could be of assistance at just relieving the restrictions imposed by supply outlets and grilles having lower free airspace. We recently reduced the noise in a clients master bedroom because the face velocity on the supply outlets was too great. We changed the outlets to a different style and the results were striking, the customer happy and all at minimum cost. So in your case, I'd recommend someone who really knows airflow and is familiar with the various supply outlets (diffusers and registers) and return grilles.
If YOU want change, YOU have to first change.
If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!