I recently sold by Cherokee 6/260 and moved into a C310Q. During the past couple of flights, passengers have mentioned how much louder the 310 is compared to the 6/260. Given this, I decided to do some math to calculate tip speeds and see if there is a true noise increase or if it is just circumstantial. The 6/260 tip speed at cruise (2400 rpm) calculated to .744 mach. The 310Q tip speed at cruise (2450 rpm) calculated to .747 mach. The 310Q tip speed at cruise (2300 rpm) calculated to .701 mach. Measuring the distance from the cockpit to the blade tip on both aircraft, the distance is similar. The only thing I can think of that would make the perceived difference in noise would be the fact that there are now 2 engines making noise and the relationship of the seats to the tip path plane. Thoughts?