Why did my PC fan get loud earlier? How to find out

When a fan gets loud, it is reacting to heat, and heat usually comes from a program working the CPU or graphics card hard. Pulse by Zaweba lets you find out afterwards: its History page has a list of temperature peaks for today, yesterday or this week, each shown with the three busiest apps in that minute. That links the noise to the program behind it.

By the time you open a monitor the fan has usually calmed down, so a live view shows nothing interesting. You need a record of what happened, and Pulse keeps one, a minute at a time, for 30 days by default.

Why fans spin up

Fans follow temperature. When the processor or graphics card does more work it makes more heat, the temperature rises and the fan speeds up to carry it away. Common causes are updates installing in the background, antivirus scans, indexing, a browser tab running heavy scripts, a game launcher patching, or a program stuck in a loop. Dust and a blocked vent make every one of those louder, because the fan has to work harder for the same result.

Finding the moment and the cause

Pulse needs to have been running at the time, so it is worth leaving it in the tray and ticking "Start Pulse when I sign in". Each minute it stores every sensor's peak and average, along with what each busy app was doing.

Open the History page (Ctrl+3) and choose the period: Today, Yesterday or This week. Look at the temperature peaks list. Each entry is a peak reading with the three apps that were busiest in that minute. If the fan was loud around three o'clock, find the peak near that time and read off the names. The CPU and memory graph on the same page shows how long the load lasted, and the Top CPU users list shows which apps used the most processor time over the whole period.

Which temperatures Pulse can see

GPU temperatures and NVMe drive temperatures are read without administrator rights, so they are recorded from the start. CPU temperatures need the optional sensor helper. Turn on Settings > Sensor readings, or the button on the Temperatures page, and Windows asks for permission to start a small helper that only reads sensors and stops when Pulse closes. CPU and motherboard sensors also need the free PawnIO driver. With the helper on, fan speeds in RPM appear in the Fans group on the Temperatures page too, when the hardware reports them.

If CPU readings aren't on, a peak in the list may be from the graphics card or a drive. That is still useful: a GPU peak with a game or a video app beside it tells its own story.

Stopping it happening again

Once you know the program, decide whether the load is reasonable. A game or video export is meant to work hard. A background updater running flat out at a bad moment may have a schedule you can change in its own settings. If you don't recognise the name, select it in the Live table and choose Open file location to see where it lives. If it is misbehaving, End task closes all its processes after a confirmation.

You can also ask Pulse by Zaweba to warn you. The temperature alert on the Alerts page fires when a sensor stays past its threshold for five seconds, using the sensor's own hot band unless you set a fixed figure. The next time the fan roars, you'll get a notification naming the hot sensor while it's still happening.