JRC uses what I believe is called a stepping motor, meaning that the motor has predefined start/stop areas as it rotates. That's how the radar knows where the antanna is positioned at any given instant. These motors, by definition, make noise not encountered with regular non-stepped motors. That noise is, in a sense, amplified through gear slap and imperfections in the nylon gear train.
If the unit sounds like it's comimg apart, call the dealer or JRC to discuss a replacement. What you're describing sounds normal, but I can't tell for sure. Normal to me means a distinct noise (which could be mistaken for grinding) lasting for a few seconds when the unit begins to rotate, and then a slight, but noticable noise during operation, but which can't be heard when the boat is underway. I'd describe the normal operating sound as having a "wobble", which is a combination of the stepping motor, and gear slap, with a periodic repeating component as the gear train drives the antenna. You pretty much have to know what you're listening for, like any noise.
You might find a few other users, and see what noise levels they experience.
If you're inclined to do a little self-help, you can access the motor and gears by removing the top half of the antenna cover (don't overtighten the 4 screws when reinstalling). Power up the unit, and see how the sounds correspond to the position of the antenna while it rotates. Then, take a popsicle stick and shape one of its edges to conform to the approximate shape of the space between the gear teeth on the white nylon drive gears. Carefully run the stick up and down between the gear teeth, along the circumference of each gear, to knock out any loose debris or gear manufacturing imperfections. This technique was recommended by JRC tech support, and it does work. If you notice any problems with the gears, call tech support, and they'll send you a set to swap out.
Good luck. I really like the 1500, and use it all the time, without maintenance.
