I would suggest you use a ball bearing servo. A bushing servo will growl when you apply tension to the wires. I have pull-pull on my Morris Fun Design. I use Futaba 3001 bb servos. They are cheap and mine have been in service for 2 years (100 to 150 flights) and no problem. Also, if you use wire, hang weights on the wire for a few days before you install it to stretch it out. Try to keep the wires as straight as possible between servo and arm. Also, use at least a double pass on the wire through the sleeve. A triple pass is recommended but the ID of the sleeve is to small.