I have 2001 Silverado with an ANNOYING buzz/grind. It worse when it's cold on startup. It seems to be some type of vibration that happens under load. It's an automatic. In 1st, under normal driving, the "grinding" is from about 800 to 1000 rpm, in 2nd and 3rd it happens when the tranny shifts up or down and the rpm is in that range.
If I'm stopped and in neutral, it makes the noise, but much softer. In gear with the brake engaged, it's loudest at about 900 rpm.
Any ideas what this could be. My mechnic said it could be just about anything which didn't help much.
Thanks for your help!