I have written a very short letter to the manufacturer. A long letter to the contractor with dates he came to try and correct the problem and the results. (I keep a fairly good diary) also asked the questions you suggested. I also contacted three other people in our area that have the same through the wall vents that have been in over 5 years. All run quietly (quieter than the fan on the furnace) and have been problem free. I have indicated all this in my letter to the contractor. I really appreciate your time and will let you know the results.
