what radio system do you have?

that is usually signs of a loose connecton, either the battery to esc wires, or esc to rx wires.

check those wires for nicks, splits and cracks. any loss of wire insolaton, will help allow rf signals to effect your radio signal or electronic gears.

it may also be a radio reciever issue.

are you postive your battery pack is fully charged, and a healthy pack? Radio batties charged and good?