Neighbors HVAC unit has a noisy problem

I knew there must be something wrong with it.

I work from home. I like the peace and quiet and I get all of my work done while the kids are in school. The TV is off and the only sounds I hear are the birds. Occasionally, I can hear one of the neighbor’s dogs bark or a kid cry. I live in a populated area so I also hear car doors close and traffic noises. Then, recently, I have been hearing what sounds like a diesel engine running, on and off, outside my house. When I go to check it out, I don’t see any big trucks. Yesterday morning, I had to get up really early. I never walk my dog before sunrise but I had to this time. After all, the dog has to use the bathroom in the morning regardless of what I have planned. Anyway, I walked the dog about two houses down when I suddenly heard that diesel engine sound again. It startled me. I was beginning to think there was a ghost truck in our neighborhood because when I looked around, there was no truck. Then I noticed that the sound was coming from one of my neighbors HVAC systems outside. I don’t know how they sleep with such a racket going on. It also can’t be normal for their HVAC system to be so noisy. I knew there must be something wrong with it. The dog did his business, I left home and did what I had to do. And, would you know it, when I got home I saw that there was an HVAC company truck in front of my neighbor’s home. I guess I was right about there being some sort of HVAC problem.

air duct