Nice to see your project here too, and welcome. Any servo will "buzz' if it is not in the position the wheel on the transmitter is indicating the servo should be. IE: The TX wheel is centered and the servo isn't. If you lift the front wheels of the truck off the ground the weight of the truck won't be stopping the servo's from centering themselves and the buzzing should stop. If it doesn't, that means one servo is "fighting" the other to get into the correct position. To remedy this you will have to adjust the links going from the servo horn to the bellcrank. They should be the same length, but it doesn't always work out exact, and you can't always silence them completely. But you should be able to get them to not make noise when there's no load on them (wheels off the ground) and they're able to center themselves.
Gearing: A nitro Revo spur gear won't work, way too small and also Mod1 instead of 32pitch. The stock Erevo spur should be the same as a stock Emaxx spur 68t. If the motor mount allows you can go with a smaller sput, I know 65T and 62T is availible for these transmissions from Traxxas. How many cells are you running? Theres also a nice gearing calculator BrianG from this forum made up to help you figure some things out.
http://scriptasylum.com/rc_speed/
Hybrid Mode
