If your sub is buzzing when plugged into the outlet, plugging it into the surge may not work. I would start by making sure that the Neutral from the outlet to the panel is not switched, nor do you have what is called a "Bootlegged" ground, which is where a person connects the Neutral to the ground screw on a outlet also, so that it passes as that there is a ground, when actually there isn't.
From there, go down to the panel, if you are comfortable with working in it, and make sure that all of the screws securing the grounds and Neutrals are tight, along with the screws for the hot to the breakers.
My guess is, that you have a questionable ground on the circuit, causing the line hum. Now of course, if you are not comfortable with playing with the electrical system, calling an electrician, not a handyman is in order. Also, contact your electrical supplier, and tell them that you are seeing problems with your electrical system, and they can check to make sure that the Neutral is correctly hooked up at both the transformer and the house.
Another item to check, is making sure that your panel is bonded to the cold water pipe, if it is copper, and if there is a water meter inside the house, there should be a bonding jumper that connects both sides that enter and exit the water meter. Also check the ground connection for tv & telephone, since they can introduce line noise if not connected to earth ground properly.
In older structures, line noise hum is common, especially if the system has not been maintained over the years, or changes have been made over the years. A new electrical system should not, if the panel and wiring have been changed in the house. I have a whole house Surge protector, and proper grounds for both my telco & POCO, so I do not get line noise problems, plus the whole electrical system in the home was updated in 2003.