Possible Causes:
* Fuel Pump: This is the most likely culprit. A failing fuel pump can make a humming noise as it struggles to operate. This humming might get louder or change pitch as the fuel level changes. A completely failed fuel pump will leave you stranded.
* Loose or Damaged Fuel Pump Components: Something inside the fuel pump assembly, like a loose impeller or worn-out bearings, could be creating the humming sound.
* Debris in the Fuel Tank: While less likely to cause a hum specifically, significant debris could be interfering with the fuel pump's operation, potentially leading to unusual noises.
* Electrical Issue: A short circuit or problem with the fuel pump wiring could also produce a humming sound.
What You Should Do:
1. Don't drive the car extensively: Continued use could damage the fuel pump further.
2. Check the Fuel Level: See if the humming changes with the fuel level. A low fuel level might exacerbate a fuel pump problem.
3. Listen Carefully: Try to pinpoint the exact location of the hum. This can help narrow down the possibilities.
4. Consult a Repair Manual: A service manual specific to your 1999 Bonneville will provide diagrams and troubleshooting steps.
5. Take it to a Mechanic: This is the safest and most reliable option. A qualified mechanic can diagnose the problem accurately and safely repair it, preventing further damage to your vehicle and ensuring your safety.
Ignoring the problem is risky: A failing fuel pump can leave you stranded. In more severe cases, it could even lead to a fire. Get it checked out as soon as possible.
