The UPS units that I currently use for our home & shop computers are line-interactive versions. They provide power regulation & surge protection until a power outage occurs or the incoming voltage is out of tolerance. Then the UPS switches to providing AC from its internal batteries. The line-interactive units produce only a small to moderate hum until they switch to battery power during a power loss, then the hum is quite noticeable. I’m considering replacing a burned out line-interactive UPS with an online UPS that continuously provides power from the batteries. For example: Tripp Lite Smart Online Model SU1000XL Do online UPS units produce a more noticeable hum than the line-interactive UPS units? Do any of you have experience using an online unit? Pros? Cons? Suggestions?