There is an expression in Japanese, shita zutsumi wo utsu, or, to smack one’s lips when eating something good. Making a sound when eating something with relish is apparently the same in Japanese as in English.
Although making unnecessary noises when eating is considered rude even in Japan, enjoying something with gusto while observing good manners is no cause for rebuke.
In the first place, Japanese food is made for slurping because there are certain foods that must be piping hot in order to be enjoyed.
Soup such as miso soup, especially, is best when just made. Because it is very hot, the lips must be brought in direct contact with the bowl and the contents consumed together with air, causing one to slurp. This goes for nabemono, a hot pot cooked at the table. And piping–hot, just fried tempura is something not to be missed!
Western–style soup is also hot, but a spoon is used and an appropriate temperature is reached by the time the soup is brought to the mouth. There is no need to slurp.
And there is also soba. There is a certain style to follow when eating soba. It should first be slurped noisily into the mouth, then shoveled all the way to the back of the throat and swallowed down with a gulp. This is the chic way.
Western foods should be eaten following rules applied to Western food and Japanese food should be eaten following rules applied to Japanese food.