Problem with low volume on one band only

Just wondering if anybody might have any ideas on this. A friend purchased a used 780. We noticed that the VHF air band is significantly lower in volume than everything else, including other AM bands,like the UHF air. The reception seems normal, but the volume is just low. Like maybe half what it should be. We compared it with mine at the same location, and with the same external gear... and his is definitely lower. It's an odd problem that I've never encountered before, and I can't seem to find anybody else that has either.

Anything?

Thanks