Ok. When I got home this evening I took another look at Galaxy 16 and saw that the carrier on 3971V was gone. This could be the source of your problem. Due to the strong transponders on AMC1 I'm gonna bet that you have to bump your dish more towards G16 in order to receive signal from SES1 and when this mystery carrier fires up on G16, bam your signal disappears. I'll try and check again tomorrow and scan it if it's present and see if I can identify it. Probably some sort of occasional feed.