99 sierra help

[79bonanza]

ok my 99 sierra has started to make a poping noise when i drive it. ive checked all my u-joints and there still good. the poping sounds like how a wheel bearing in a old solid axle truck when its going out. the noise is coming from the mid to front under the truck. also it doesnt do it nearly as bad as when its in 4wheel drive. any ideas on what it could be

 

[DeviousK5]

Based soley on the brief description and the ease of checking. There is a snapring on the rearmost portion of the t-case output shaft that tends to up and break and can pop or grind, especially worse when on the gas hard. Not 100% sure if thats your problem, but simply removing the driveshaft and tailhousing portion of the t-case and checking to see if the snapring is still intact would eliminate that possibility. Plus its super easy to check .
Sorry if that doesnt help in any way

 

[79bonanza]

ok ill check that. more details the sound started out like when your rear brakes are warped and are just brushing the rotor but then it went to a poping sound. and the truck has a 4 inch suspension lift and 35's on it.