The noise you hear is liquid freon passing through the orface or expansion valve then "boiling" in the evaporator, it continues after you shut down until all the liquid freon has boiled off, all perfectly normal, all cars do this. On some cars this noise is louder than others. It does not necessarily indicate any problem. If it is cooling normal there is nothing wrong.

If the noise comes and goes while driving in very short cycles (say 10 seconds) you may be low on freon. However you said after shut down it continues for one minute. If the boiling continues that long you are not low on freon.

For piece of mind let the shop have a look. No problem to continue driving.
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David Hunter