G-r-r-r-r-r-r-r-r! or R-o-a-r! are some sounds that a bear makes.
AwAw
The polar bear makes a 'Growl' sound
ROAR!
The sound a flute makes is typically spelled as "whistle" or "flutey."
rowr!
The sound a penguin makes is typically spelled "hok hok" or "bray."
Varooooom
The sound a buzzer makes when the answer is wrong is typically spelled as "bzzz" or "buzz."
The typical written expression for a yawn sound is "ho hum."
Ka-ching!
Baa.
vroom
Unnh!