That is the alternator whine for sure. I have an 08' and I can tell you that there is almost no way you can damage the GL1800 engine!
If you could go into the bikes CPU and harvest the data from mine, you would see most of my highway miles are in the 4000rpm range. Average commute speed is around 90-100
I ride it HARD a lot, probably too hard but it doesn't seem to mind the abuse and sounds/runs today, 10k miles later like it did the day I rode it off the showroom floor!
Matter of fact, I am on the forums a lot, here and elsewhere, and I do not recall a single thread where someone blew an engine. Well except for the guy who turned his wing into a GL1800 Turbo, that one did not last long from what I heard.
I would not be scared to buy any GL1800 that ran smooth, shifts thru the gears fine and looks taken care of.
Buy one and ride the crap out of it!