In case of the geared motor (ac, parallel type), Is there any difference on noise level as per direction of rotation (CW, CCW)? could you let me know the reason?

Helical gears in the reducers reverse their axial loading direction.

Ditto Jeffrey,

Many small geared motors have bronze sleeve bearings which can allow some axial movement when the axial load reverses.

Thanks a lot....Mr.Jeffrey & Mr.Barry..
above tips are so helpful to me..

I've delt with a sumotomo cyclo gear reduction motor and gear box and can't seem to differentiate noise levels from forward to reverse, with a smooth transition in direction.this is with 4 motors running off of one drive in parallel with resistor type braking system.

Also the junction between the motor and gear box has a planetary coupling system.

No it will not,whether parallel or inline,the noise level will b same,unless the grinding is not done properly it may produce noise.