I just tested my amp, little gem mark2. It's outputting sounds, but theres a popping noise coming from the speaker every few seconds. It happens more frequently when I turn the volume on my guitar up or when I increase the gain on the amp, but it still happens when the volume is turned down and when the drive is mostly off.

Is this what oscillation is? Because if it is, than I know how to fix it, a 47nf capacitor from pin 7 to earth. Would this be just my dodgy soldering? Could it be my lead, which I just got fixed today (sadly it's my ownly lead)? Could it be that I'm using a 8 watt speaker for a 1.5 watt amp?

And here is my amp schematics:

Thanks in advance
[U]        | |                     [/U]
[U]        |/     .-.              [/U]
[U]       /|_     `-’       |      [/U]
[U]      //| \      |       |      [/U]
[U]     | \|_ |     |     .-|      [/U]
      *-|-*    (_)     `-’
Sounds a lot like a leaky capicitor to me. Instead of storing the electrons till the tension in the lead drops enough to discharge in the direction the current came from, it discharges through the foil over the other lead whenever a critical threshold is reached. The higher the voltage, the sooner this will be, so it makes sense that the frequency goes up when you crank up the volume.
Dodgy soldering could well be a cause. Maybe you've had the soldering iron on it too long and fried the poor bugger to death. But too high a load can also distroy them and every once in a while a brand new one proves to be dead right from the start.
Luckely there are only five of them in this circuit, so it must be no big problem to pick the culprit out.
Try another adapter first and see if it still happens when no guitar is plugged in to rule out the possibility that the problem is caused there.