Do you have access to the underside of the stairs? Sounds to me like they were not built or shimmed properly but would need to see some sort of pics for anyone to offer any suggestions.

Check your humidity in the home. Wood based subfloors and stairs OFTEN creak when the humidity in the home is NOT high enough. Does your home have a whole home humidity control panel? We call it a humidistat and you can change the humidity with a touch of a button. You want to see readings between 45% - 55% on a daily basis...for the rest of the home's life.

The house is brand new, it was a new build and we just moved in about 1.5 months ago. It is actually our guest room and office underneath it. Whenever someone is walking upstairs you hear the creaking really loud in the office beneath.

See if you can answer the above questions, honestly that is the only way anyone can offer suggestions.

Is there carpet in the area that squeaks? If so, it seems unlikely that the floor company is responsible for a squeaky subfloor. Call the builder to fix. If it's wood floor, it's still rather likely that the subfloor is the culprit.

Ok, here are the answers, please let me know if any more info is needed.

I do not have access to the underside of the stairs.
We only have the generic Honeywell thermostat.
There is carpet. The contractor said they will be calling the truss company next.

"The contractor said they will be calling the truss company next."

Why would they call the truss company? I would get a hold of the builder and the stair builder. Between this two is where the issue lies period.

Is this only in one room upstairs? Or in all rooms. I know you would most likely only hear one room when in the office, but, how about when someone is in different areas, and someone walks over their heads?

It is the only one we can hear. We have a loft above the kitchen and there is no noise there.

Well, maybe have the carpet removed, and have the builder remove the sub floor and make sure all is ok underneath. He can relay the sub floor, and maybe add more screws too, and then have the carpet relaid.

You are talking upstairs as in on the second floor. I misunderstood I thought you meant the STAIRS were creaking not the upstairs.

this old house solution. This segment was on a carpeted surface, there is another episode with a hardwood floor