Before jumping to conclusions about the fuel pump, consider these other possibilities:
* Differential: The rear differential is located in the back of the vehicle and whining noises are a common symptom of failing bearings or low gear oil. This is a very likely culprit for a whining sound.
* Wheel bearings: A worn wheel bearing can also produce a whining sound, especially at higher speeds or when turning.
* Exhaust system: A leak or restriction in the exhaust system, particularly near the rear, could create a whining or whistling sound.
* Alternator (less likely): While typically associated with squealing, a failing alternator *could* produce a high-pitched whine under certain conditions.
Why relays are less likely: Relays themselves don't usually make noise. A faulty relay might *prevent* the fuel pump from working (leading to a lack of power, not a whine), but it wouldn't cause a whining sound on its own.
What to do:
1. Check the differential: Listen carefully with the vehicle running. If the whine changes with vehicle speed or when turning, the differential is a prime suspect. Check the fluid level and condition. Low or dirty fluid can cause a whine.
2. Check the wheel bearings: Jack up the rear wheels one at a time and check for play or roughness in the wheel bearings. If you can easily move the wheel up and down or side to side, the bearing is likely worn.
3. Inspect the exhaust: Look for any holes, rust, or signs of damage in the exhaust system, particularly near the rear.
If after checking the above, you still suspect the fuel pump:
* Listen carefully: Try to pinpoint the exact location of the noise. Is it definitely coming from the fuel tank area?
* Fuel pressure test: A mechanic can perform a fuel pressure test to determine if the fuel pump is delivering adequate pressure. This is the best way to diagnose a fuel pump issue definitively.
In short, while a fuel pump *could* be the source of the whining, other components are far more likely culprits given the description. Start with the differential and wheel bearings. Only if those are ruled out should you focus on the fuel pump.
