I know that more work feeling, but for me it was TI-83's (I think) and I rarely used the programs I wrote. I was quicker doing most work(80%) in my head and using paper to make sure it looked correct.
So why did I write the programs at all? Boredom, really. It was also a good way to make sure I really understood formulas - if the calculator was wrong, I made a mistake or typo.

Depends on the bike, I guess. Something bare-frame, Harley-Davidson stylish (more open frame type) would be harder to hide stuff on. Something like a Goldwing 1500/1800 or any plastic-paneled type bike, you could try to hide alot more in there.

I have.. my first fake command line was in DOS, ages ago. My poor friend didn't let me touch his computer for a long time after that..

The hf sound theory is a good possibility, speaking from personal experience. I can hear the high pitch buzz from crt's (probably the transformer in them?) and similiar sounds, but tv buzz is the only source I can always pinpoint. Probably because my tv doesn't move. Not sure the exact frequency of the buzzing, never was good at figuring exact khz stuff by ear.

And for the record, it doesn't cause me any annoyance and I don't want to sue anybody over it.

And trying again...