Hi,
Good airflow just means that the fan is working but it doesn’t mean that the fan isn’t noisy when it is operating.
A whirring sound is more likely to come from it, as it is the only component that is physically moving inside the laptop.
Here’s the ifixit [guide|99839] guide that will help you to open the laptop so that the fan can be checked etc.
As regards viruses, even though they can infect the Chrome OS, Google has tried to make it hard for them to cause any problems. Here’s a [https://support.google.com/chromebook/answer/3438631?hl=en|link] that explains what happens. Also this [https://platypusplatypus.com/chromebooks/scan-remove-viruses/|link] gives an in depth insight into the Chrome OS and viruses and malware