When I try to cut with my mains-powered (plugged-in) trimmer, it makes a loud noise. What's happening?

This means the blades require lubrication or the power screw on the right side of the clipper needs adjusting. To calibrate the machine, plug in the clipper and turn it on. Then, turn the power/voltage screw counterclockwise until the noise decreases to a standard operating noise. Next, adjust it another quarter turn. If adjusted correctly, this should resolve the issue. Alternatively, consult your instruction booklet.