I also have this problem - it sounds like someone is playing a kazoo in my driver's side view mirror. Very irritating and seems to be exacerbated by colder temperatures. 2.0T Touring, here.
Well, since a mirror is mentioned, you should know there is a TSB about noises from the driver side-view mirror. It is not installed correctly at the factory and the seal at the base is loose. The dealer can check for this and fix it.
You guys should really check out the Service Bulletins ("Manufacturer Communications" as NHTSA calls them these days) on the NHTSA web site. You should also read about all the complaints others have made to the NHTSA about their Accord.
I think you need to search by "2018 Accord Hybrid", and not just "'Accord" like I did for my Sport 2.0 - if you have the Hybrid model that is. They do not differentiate between trims like "Touring", EX, Base or Sport models, when it comes to Recalls and TSB's, but they do differentiate between the regular gas Accord and the Hybrid Accord because they are like 2 different models.
I think I did a search on the NHTSA for the Hybrid as well and remember reading something about a noise from the trunk where the batteries are? There were NOT many complaints on the Hybrid. You guys will have to check and if the dealer is not helping you, fill out the complaint form on the NHTSA web site. If they get enough complaints Honda will act.