A buddy of mine is having issues at his house. I am pretty handy, so he asked me to take a look. Basically, when he runs the washer and the dryer at the same time, the lights in the house will flicker a bit.

When I inspected the situation, the washer and the dryer were plugged into the same 120-Volt receptacle. The dryer is a natural gas dryer, so I figured this was okay (i.e., not too much power for a single receptacle).

Next, I inspected the electrical panel. The panel mostly contains aluminum wires, which is not anything that I have ever experienced before. The circuit with the washer/dryer is definitely a thicker wire than the other wires in the house. I could easily re-wire the circuit in question using modern, copper wire. It would require about 25 feet of wire (if that) and it'd take me 30 minutes (everything is exposed, so pretty easy).

That said, any other suggestions as to the cause of the lights flickering?

I suspect the washer/dryer wire is #10 aluminum, which is the correct size for a 20 amp circuit using AL wire. Inform your friend, if there is ever a property insurance inspection of the building, one hot item is aluminum wire, and they will require actions taken to mitigate the condition. What usually happens is the lights that are on the same circuit will flicker. Can you determine if the the lights that flicker are on the same circuit? If no lights are on the circuit, there are other issues.