Does it bother my goldfish with the fountain pump running 24/7 ? The
output is adjustable and the pump is rated 600 GPH, in a 20 gallon
barrel liner. I do not find the 2 goldfish getting disturbed by any
turbulence with the fountain height (2-3") that I prefer, but does the
splash/bubble/noise get to them?

When I turn the pump off I can see the fish out more often but then it
could be because I am having a better ability to see them.

I had reduced it to a slow trickle until I can get better answers.

Does it shorten the pump's life to restrict it's output?
Does it generate more heat?