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220-1201 Practice Question: A technician is troubleshooting a PC that emits a…
A technician is troubleshooting a PC that emits a high-pitched whining noise under load. The noise is coming from the power supply area. The system is stable and temperatures are normal. What is the most likely cause?
⚠ Common exam trap
Watch out — candidates often confuse coil whine with fan bearing failure — both produce noise from the PSU, but the key differentiator is the pitch and the system's stability; candidates who focus only on 'noise from PSU' without noting the high-pitched quality and normal temperatures may pick the fan option.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The PSU is experiencing coil whine due to electrical resonance.
Coil whine is a high-pitched noise caused by electromagnetic resonance in the PSU's inductors and transformers when current flows through them under varying load. It is a benign acoustic artifact — the system remains stable, temperatures are normal, and no protective shutdown occurs, which matches the scenario. Fan bearing failure produces a grinding or rumbling noise, not a high-pitched whine, and thermal protection would trigger shutdowns rather than just noise.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The PSU fan bearing is failing.
Why it's wrong here
A failing fan bearing typically manifests as a grinding, buzzing, or rattling sound, caused by friction or wear within the bearing assembly. This mechanical noise is distinct from a high-pitched electrical whine and would likely be present consistently or intermittently, regardless of the PSU's electrical load. It would not specifically correlate with changes in power demand.
- ✓
The PSU is experiencing coil whine due to electrical resonance.
Why this is correct
Coil whine is an audible high-pitched sound originating from the rapid vibration of electromagnetic coils, such as inductors or transformers, within the PSU. This phenomenon occurs when electrical current passing through these components causes them to resonate at frequencies within the human hearing range, often under specific load conditions or power states. While potentially annoying, it is generally considered a harmless byproduct of electrical resonance and not indicative of a failing power supply unit.
- ✗
The PSU is overheating and the thermal protection is activating.
Why it's wrong here
If a PSU were overheating and its thermal protection was activating, the primary symptoms would involve the cooling fan spinning at maximum RPM, or the system initiating an emergency shutdown to prevent damage. Overheating itself does not directly produce a high-pitched electrical whine; rather, it triggers protective mechanisms that are distinct from this specific acoustic signature. Furthermore, the problem description states temperatures are normal, ruling out thermal issues.
- ✗
The PSU has a loose internal component rattling.
Why it's wrong here
A loose internal component, such as a screw, cable, or small part, would typically produce a rattling or clunking sound, especially if the PC is moved or vibrated. This mechanical noise is distinct from a consistent, high-pitched electrical whine and would likely be present more broadly, not specifically tied to the electrical load or resonance conditions that cause coil whine.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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