TX audio distorted after a few days being on.

I have a 6400 that has very bad tx audio distortion. I have had it less than six Months. Apparently this tx distortion issue is occurring back in 2020 too and has gone unresolved escaping their test process perhaps going on three years. My 6400 is at flex now 4/2023 . It cost me $145 to ship it to them. Their early analysis is their test process; I was told, performed with two dummy loads and a reference receiver testing using 6 Meter band that it has not failed their 6 Meter band two test tones audio test. I told them I don't use 6 meters. I am experiencing tx audio distortion on 40 meters and 80 Meters which are the only bands I used so far. I don't know if they will test my radio using 40m and 80m. Their Test engineer told me he just tests at 6 meters. I hope they will check it at 40m and 80m while they have it on the bench. They should test 160m 80m 40m 15m, 20m. 12m 10m and 17m as well in my opinion. I suggested it too them. I don't want have to send it to them a second time for same tx audio distortion issue. Too costly shipping it to them. Besides hat would be a better more complete test process in my view any way. They gave me no indication would add these band tests to their test suite, but I hope convinced them it a reasonable idea to do add all bands tx audio test. If they can't reproduce the tx distortion using 6m band only it seems logical to test my radio at 40m and 80m at least since that is bands causing the distorted tx audio failure in my shack.