I'd say 19 times out of 20 or maybe 49 times out of 50 or maybe ... (well, you get the idea), you will be OK. But sooner or later the odds will catch up with you even if you have a drive that will automatically park the heads when you are not reading or writing.
But they are not THAT fragile or laptop computers would not be that practical.
On my old laptop I was never worried about this... I just bought a new laptop, and when I picked it up and turned it on its side to carry it, I heard some noise (probably a fan or something?), but that got me wondering about this
Anyway, how hard of a bump would it take to ruin it?
any bump could ruin it, depend on timing and location. I can't give you an exact force measure, but I've had a laptop fall to the floor from table (about 3-4ft) and the laptop weighed about 3-4 lbs, it is fine to this day.
The noise youre hearing when picking it up is most likely a fan (if it's high pitched, if it's a low pitch sound, it could be HDD motor but I doubt it's a big problem)
what is your problem with bumping in general? did you bang some laptop and it's not booting up? or you plan to do it in the near future?
rule of thumb: treat your electronics nicely and they will live a long and good life serving your needs. if you go bumping, dropping and otherwise mistreating your electronics, well, don't be surprised if you're shopping for a new laptop within 2 years.