There's no plastic in an aluminum can. Both glass and aluminum are almost totally recycled into their base materials. Aluminum is lighter to transport to and from the recycling facility.
That is a good question, but I suspect if you tried this in real life it would still show static.
The waves are amplified with a circuit that attempts to find a signal even if it's very weak (so you can get a picture even if you're close or very far from the tv station)
At a certain point, the electromagnetic field from the running TV itself would start to get picked up
I suspect a better thought experiment would be if you just disconnected the input and amplification circuit entirely from the CRT tube, in which case you would probably just get white as the electron beam scans back and forth without any modulation.
Dental Plan!