If the multimeter probe causes the same problems, connect the scope across the gate and source to see what changes when you touch the drain.
The first, low amplitude waveform may have been noise. It wasn't a good drive. Touching the drain may simply have triggered the rail-rail oscillation which caused the increase in current.
You can also try simply driving a signal into the amp to see if that makes the same changes as touching the drain.
The first, low amplitude waveform may have been noise. It wasn't a good drive. Touching the drain may simply have triggered the rail-rail oscillation which caused the increase in current.
You can also try simply driving a signal into the amp to see if that makes the same changes as touching the drain.