Removed a lot of the excess silicone around the IQ Air and returns connected to the furnace. Applied a new bead of silicone so not so much extra was left. Homeowner believed the excess silicone is the cause of the smell. I inspected and did a pressure drop test on the IQ air filters and did not find them to be in bad shape. I also inspected the ducts and returns to make sure these were clean also. Both looked good