Upon arrival tenants stated system makes a knocking noise and they have since turned the system off. Tech ran system from thermostat and did not notice any noises inside building. System cooled until reaching set point. No rooftop access in riser room. Tech used extension ladder to try and gain rooftop access. However, tech was unable to due to wind and rain. Tech informed Ms. Suzy. Will need to come back to inspect system on rooftop. Billing out for service call fee. Also need to get in contact with Ms. Suzy for CMA quote.