Device behaviour, cause for concern?

[Oakey]

Over the last few weeks, maybe longer, I've experienced the following with our laptops and mobile phones:

Laptops would suddenly be on mute when previously they hadn't. You'd put the volume up and after some time they'd randomly be on mute again.

Screen flicker when you'd move the mouse.

Increased network activity

Increased Hard Drive activity when there shouldn't have been

Sudden increased CPU activity even though the laptops weren't being used, causing the fans to run at full power.

Slow and sluggish responsiveness, again, when there really shouldn't have been

Very quiet audio from the laptop audible throgh earphones.

As above but what could be clearly made out as previous conversations between me and my girlfriend

The very quiet sound of delayed keystrokes coming back through the laptop speakers when you were typing

Mobile phones being hot even after long periods of inactivity

Mobile batteries running down quicker than they should have.

Mobile illuminating for no reason

Alerts we'd received texts (a lot of time in the early hours of the morning) and when checking there'd be nothing there.

My HD7's MAC address changing a few days after I bought it, adding the now new MAC address so it could access the WiFi and then days later whilst checking devices in the router seeing at least 10 unknown connections, all with their own IP, but all with the HD7's MAC address.

[Moby-Dick]

you'd better call ...

[Phage]

Changing MAC ? Very odd.
The increased HDD activity can be anything include Windows doing it's cataloging in the background, AV or auto updates running.
I assume you're running some AV solutions ? I assume that the Router has a strong password and is running the highest level of encryption ?

[Oakey]

I had the router setup to MAC address access only but I'm currently revising this.

The muted audio on the laptops and screen flicker did make me wonder if someone was using remote desktop?