Most Likely Culprits:
* Worn-out differential: This is the most probable cause. The differential gears are responsible for distributing power to the rear wheels. Worn teeth will grind and cause the noises you describe. This requires a complete differential rebuild or replacement.
* Worn-out pinion bearings or carrier bearings: These bearings support the differential components. Wear can lead to grinding and play in the drivetrain. This is also a major repair involving differential disassembly.
* Broken or damaged ring and pinion gears: More severe than just worn gears, a broken or severely damaged gear will create significant noise and potentially damage other components.
* U-joints (universal joints): While less likely to cause a grinding noise specifically *in reverse*, worn U-joints can contribute to a clunking or thumping sound, especially under acceleration. These are relatively easier and cheaper to replace than differential work.
* Axle shafts: Worn or damaged axle shafts can create a clicking or grinding noise, especially under load.
Less Likely (but possible):
* Wheel bearings: While more likely to manifest as a humming or rumbling noise, severely worn wheel bearings could contribute to the overall grinding sensation.
* Brake components: While unlikely to cause a grinding sound *specifically* in reverse and under acceleration, something like a stuck caliper could contribute to unusual noises and resistance.
What You Should Do:
1. DO NOT drive the vehicle extensively. Continuing to drive with a damaged rear differential can cause catastrophic failure, potentially leading to loss of control and serious damage to other components.
2. Get a professional inspection: Take your Tahoe to a qualified mechanic specializing in drivetrain repairs. A visual inspection, and possibly a road test (carefully done), are crucial for accurate diagnosis. They might use a stethoscope to pinpoint the noise source.
3. Be prepared for a significant repair cost: Differential work is expensive. Replacing a differential, rebuilding it, or even replacing individual components within the differential can run into the hundreds or even thousands of dollars.
Before you take it to the mechanic:
* Check your differential fluid: Low or severely contaminated differential fluid can exacerbate wear and damage. However, this is unlikely to be the *sole* cause of your symptoms. A visual inspection of the fluid can reveal contamination (metallic particles).
In short, ignoring this problem is not an option. Professional diagnosis and repair are essential to ensure your safety and avoid further, more costly damage.
