My reading indicates that water hammer is caused when a water source is
turned OFF.

Last night, we turned ON the dishwasher and there was a loud rumbing
noise. I went downstairs and saw the hot water line (downstairs is a
garage with exposed piping) shaking/vibrating pretty severely. This
stopped whenthe dishwasher started washing. No further problems later
when it entered the rinsing cycles.

Given this was our first experience with what I assume to be water
hammer, can anyone confirm that water hammer may occur if a
faucet/water appliance is turned ON? thanks.

-JC-