Yes, I did email to the company to ask for help. I got the following feedback from the owner, Allan who is quite helpful. I am reposting it here with the hope that it may be help someone else with the same problem. I have not got a chance to try it yet. I'll report back if it works after I have tried it.
"well the clicking noise can come from 2 things. They could have made your chain too long or too short [I recently replaced the bicycle chain, I am just not sure how would this effect the gear hub?]. If you have the old chain it should be exactly as long and have the same number of links. But if your chain is ok then try applying some very light chain oil over all the moving parts and the chain. The final thing you can do is adjust the chain tension screw located at the middle bottom of the chain gaurd.
You will see a hex head screw there ---- Turn it all the way clock wise until it gets a little tight. then go counter---clockwise back 1.5 full turns or 360 degrees plus another 180 degrees turning back counter clockwise. This is the standard setting ! If it still clicks then change the setting a quarter turn at a time and try the bike until it stops clicking. Usually the 1.5 turns counter clockwise is the perfect setting for a new chain !
Also, oil the chain and all sprockets once a week ! Use a very light chain oil that does get goooey and don't forget about not getting oil on your disc brakes. Thanks, Alan at Busettii "
From their website, I got this description. It said that the bike has 9 speeds total. 3 on the rear hub and 3 auto. So now I am not sure if the noisy slipping sound is from the rear hub or the auto gear in the motor itself. If the motor gear is having problem then I am just not sure how to fix it and the replacement cost for the motor is more than $800. Also I am confused about the claim of 1000W on a 500W motor. May be someone here can figure it out.
from http://busettii.com/vortex-2012-blue-38 ... 23810.html
Now comes in Blue OR Red & 1 or 2 batteries ! Super heavy duty Busettii mountain bike center mounted motor, real transmission (auto 3 speed) chain pedal integrated drive train for smooth pedal assist at very high speeds, Comes with both pedal assist and throttle mode,(also see http://www.biyadii.com
) 500 watt motor plus real transmission = 1000 watts of equivalent torque but just using 500 watts(compared to hub motors) Comes with 2 x 38 volt 10ah batteries (= 20 amp hours) with the high efficiency motor and trany can go 86 miles in pedal assis. mode or 60 miles with no Pedaling at all. Unlike most other e-bikes, Vortex Rider can pedal with motor even at 30 mph because of integrated drive pedal train system. Most other E bikes don't have high enough pedal gearing to stay up with motors at high speeds but Vortex solves this problem. Your pedaling always has a big contribution at any speed. Top speed 32 mph. ----Avid Disc brakes front and back ----Great Shock absorbers ----Dual 3 speed internal gears for 9 speeds total. ----Comes with on baord computer panel that shows Battery level, Pedal assist level, kill switch, on/off mode, auto shut down, energy efficiency level and Head light on/off button. Threadless front end by Huer with full angle and height adjustments. Built in cruise control and brake integrated kill switches. ----------Shows the new BLUE model with one battery but you can either color and 1 or 2 battery models. Now using BYI DEEP cycle Lithium batteries made in the USA for much longer range and better power levels. -----Free to choose Tires and frame sizes : 17" fits 5'--7" to 5'--11" and 19" fits 5'--11" to 6'--3" tall riders."