I have 21’ envision avenir . Once I hit about 5k mileage . I notice a knock/pop sound coming from engine area. It first started happening in the middle of engine area when I would put the car in any gear . Then it started making the same pop/knock sound when I would be driving the car , for example- slowing down at a light or taking off . So now we have these sounds coming from two areas in the engine area . We took car to one dealership and the tech said he drove it and heard nothing . But as we were leaving the service adviser stopped us and told us he heard it and he would write GM to find out . We never heard from them again . So we asked our daughter who works at another GM dealership if she could ask a service adviser there to see about bulletins on this issue . He found one . Everything we were saying is happening was listed on that bulletin. So we took my car to that dealership. They kept my car for 5 days . I got tired of waiting so went up there . Only for them to tell me they didn’t hear it. I have it recorded many times so I could show them and all they say is I don’t know . So I called GM myself and they contact the dealership and in the dealership notes only said ‘ need more time with car ‘ . The sound is getting worse but I don’t know what to do ?