Some useful info with  pics and repair procedure in pages 2-5  in this GM service bulletin. Here's the link:

https://static.nhtsa.gov/odi/tsbs/2019/MC-10165090-9999.pdf

Service Bulletin

Bulletin No.: 18-NA-183

Condition 1: Some customers may comment about a squeaking and/or clunking noise coming from the rear of vehicle.

Condition 2: Some customers may comment about a squeaking noise coming from the rear of vehicle.

Cause 1: This condition may be caused by debris getting between the leaf springs and/or looseU-Bolts.

Cause 2: This condition may be caused by a faulty spring shackle.

Correction 1: To correct this condition, re-torque the U-bolts of the leaf spring assembly, and install new rear leaf spring inserts, following the procedure below.

Correction 2: To correct this condition, replace the rear shackle following the procedure below.