Hello lizzyh19,
Thank you for posting in the Apple Support Communities. I understand you're hearing white noise from your Mac speakers.
The steps in this article are a great place to start: Get help if the internal speakers on your Mac don't make sound. If you find the audio stops again, I recommend checking out the "Check your sound settings" section of the link. This will give you a bit more information about what might be happening. Updating to the latest version of macOS, macOS Mojave specifically, is also a great idea. The link above has the steps you'll need to make a backup of your Mac and update.
There are two quick resets you might try as well. Resetting your NVRAM and System Management Controller won't affect any of your personal data, but can help clear up issues with audio output. When you reset your NVRAM, you may need to go back into System Preferences and re-adjust some settings, like your brightness and resolution. For the steps, check out the links below:
Reset NVRAM or PRAM on your Mac
How to reset the System Management Controller (SMC) on your Mac
I hope these steps help!
Take care.
