The combination of an unusual mechanical noise and random shutdowns strongly indicates a problem with the computer’s cooling system . A cooling fan with worn bearings, accumulated debris, or physical obstruction can produce a grinding sound.
When the CPU fan cannot rotate properly, airflow decreases and the CPU temperature rises. The computer may then shut down automatically to protect the processor and motherboard from thermal damage. Therefore, among the available answers, CPU overheating is the most likely cause of the shutdowns.
The other answers are less appropriate:
An improperly installed graphics card is more likely to produce a blank screen, display artifacts, crashes, or failure to complete POST.
Damaged RAM commonly causes application crashes, POST errors, blue screens, freezes, or data corruption, but not a grinding sound.
CompTIA objective 5.1 associates overheating, random shutdowns, and unusual noises with motherboard, CPU, power, and RAM troubleshooting. Dell identifies fan problems as causes of noise and overheating, while SSD documentation confirms that SSDs have no moving mechanical parts.
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