When you say you've checked the outlet, do you mean you've tired others? I've seen some strange issues when not using a good quality Surge Protector. I don't know where you live in the country, but not all power grids are created equally. If you have a sub par protector, or you're just plugged straight into the wall you can have issues with tiny surges knocking out or weakening passive components inside your devices causing you to have grounding issues or interference etc. (seemingly when everything looks okay inside).
Living in Florida with all the thunderstorms, almost every time after a storm I see a handful of customers with strange power/battery issues in their devices. Not ones that completely destroy the device. But issues that seems to be caused from power management IC chips going bad, weakened resistors/capacitors etc.
Again, this is like worst case scenario. But it's got me thinking that you checked all your I/O and still have the same issues.
Because of all the customers I see with these issues, I've been eyeing some Pure Sine Wave UPS options for my computer/sound setup. I cant have this stuff getting knocked out by a storm!