* Alternator: A failing alternator bearing can create a high-pitched whine or hum that increases with engine speed. This is a common culprit.
* Power Steering Pump: A worn-out power steering pump or its pulley bearings can produce a similar howling noise, especially under load (like hard acceleration which requires more steering assist).
* Belt Tensioner/Idler Pulley: These components guide and tension the serpentine belt. Worn bearings within them can cause a humming or whining sound, especially when the belt is under increased stress from hard acceleration.
* Wheel Bearings (less likely, but possible): While usually associated with noise while driving at speed, a severely worn wheel bearing *could* contribute to a hum that's more noticeable under hard acceleration, especially if the added engine load affects the wheel's rotational speed.
* Transmission (Automatic): A problem within the transmission, such as a failing bearing or worn components, might produce a humming or whining sound under load. This is less likely to be a high-pitched howl, but more of a deeper hum.
* Differential (Rear-Wheel Drive): Similar to the transmission, issues in the differential of a rear-wheel-drive Bonneville could create a humming sound, especially under acceleration. This is less likely to be a high-pitched howl, but more of a deeper hum or whine.
Troubleshooting Steps:
1. Listen Carefully: Try to pinpoint the location of the noise as precisely as possible. Is it coming from the front of the engine, the rear, or the side? This will help narrow down the possibilities.
2. Check the Belts: Visually inspect the serpentine belt for cracks, fraying, or glazing. Also, check the tensioner and idler pulleys for play or rough operation. Try to wiggle them; excessive play points to worn bearings.
3. Listen with the Engine Off: Sometimes, you can isolate a bad bearing by spinning the pulleys by hand and listening for rough spots or noises. Be careful when doing this!
4. Professional Inspection: The most reliable way to diagnose the issue is to have a mechanic inspect the vehicle. They have the tools and experience to identify the source of the noise accurately.
Ignoring the noise could lead to more serious damage and potentially dangerous situations. It's best to address it promptly.
