Right, servos don't have shift, that's only an issue between the TX and RX. Between the RX and the servos, they are all the same. I've flown more than one plane with a mix of servos of several different brands with no problems.

it's probably like Rodney said. Another thing you can check is take the servo arms off of the servos, so they have absolutly nothing keeping them from turning. Now see if the noise is reduced. While you have the linkages disconnected, move them with your hand, and you can feel what the servo is working against. Hopefully not much friction.