I just picked up a new 2013 model year 6HP Tohatsu 4-stroke with integrated fuel tank, and I've got just over 6 hours on it so far (installed a tach + hour meter before running). It's on a 13' aluminum boat with a wood-encased transom. Right about 3000 rpm it starts making a loud noise that is hard to explain, more of a ringing than a screech, but very loud. Below 3000rpm there is no noise, and by about 4000 rpm the noise is gone. It only happens in forward gear, not in neutral. I have been unable to isolate what part of the motor the noise is coming from. I ran it with the cover off and there was no change in the noise at all, volume or pitch. I thought it might possibly be the boat, but the transom is covered both front and back with wood, and I've been unable to identify any part of the transom that is vibrating at that pitch. The motor runs absolutely great, I'm just concerned by the noise and I'm wondering if something is wrong or if this is just a trait of this motor. Does anyone else with a 6HP notice this same noise at about 3000 rpm?
