Possible Causes of Grinding Noise:
* Valve Train Issues: This is the most likely culprit. The grinding noise could be coming from worn rocker arms, worn lifters, or a stuck valve. The added load from the alternator could be momentarily relieving pressure on the valve train, causing the noise to disappear.
* Alternator Bearing Issues: A bad bearing in the alternator could also make a grinding noise. However, this noise would likely be consistent, not just when the alternator is under load.
* Other Engine Components: While less likely, other components near the valve cover could also cause grinding, such as the timing chain, timing belt, or even a loose bolt.
What to Do:
1. Safety First: Never work on a running engine. Make sure the car is parked safely, and the engine is cool before you start inspecting.
2. Listen Carefully: Try to pinpoint the exact location of the noise. Use a mechanics stethoscope or a long screwdriver to listen for the noise.
3. Visual Inspection: Inspect the valve cover for any obvious damage or loose components. Look for any oil leaks or signs of wear.
4. Professional Assistance: If you are not comfortable diagnosing the problem yourself, take your car to a qualified mechanic. They can use specialized tools and their expertise to determine the root cause of the noise.
Important Notes:
* Don't Ignore the Noise: Grinding noises are usually a sign of a serious problem. The longer you wait to address the issue, the more damage and potentially expensive repairs you may face.
* Consider the Age of Your Car: A 1990 Cressida is a relatively old car. It's possible that other components may be nearing the end of their service life and could contribute to the grinding noise.
Remember, I am not a mechanic and cannot diagnose your car's specific problem. If you are experiencing a grinding noise, it's best to consult with a qualified mechanic for diagnosis and repair.
