It sounds like the Cary might have a tube, or something that gets noisier with heat. But, trying the below options might help.
On the electric part, try plugging in a portable electric heater in the same outlet, and see if the noise starts quicker due to the homes electrical parts warming quicker. This may help diagnose the outlet circuit wiring, and the possibility of a circuit breaker (in breaker panel for home) making poor contact after some warming up.
Also, try a 25 to 50 foot, maybe a 14 gauge or 12 gauge extension cord, and try plugging it into different outlets in other rooms. One may be on the other phase leg, and not have the noise in it, if it is an electrical problem.
A poor connection could occur at your electric service entrance also. A neutral in the breaker box, meter socket, or the utility wire connecting your house. The utility company might check your meter connections, and their connection supplying you, if you really think it's there. Light bulbs getting too bright and burning out would be a sign of a poor neutral connection in this area.