My GMC Sierra makes this noise only over dips. It is a 4x4 but not lifted and does not have any off road package. Any ideas what could be causing this? My long time Indy mechanic closed his shop recently and I haven’t had time to find a new one. The truck has seen a lot of trailer towing (32’) and rough roads but has only 30k miles. It has standard shocks not the magnetic ones on the Denali.