I would try letting your beer clear a bit, rack to secondary and then do your dry hopping. Stan Hieronymous wrote an article in Zymurgy earlier this year about dry hopping experiments he did. The takeaway was that he felt that hop aroma and flavor was better in beers dry hopped this way. The reason: dry hopping in primary with a fair amount of yeast still in suspension can produce some undesireable aromas/flavors from the interaction of hop compounds with excess yeast. I switched to doing this and I like my hop aroma/flavor better than before - it seems cleaner and better. I'd be curious to see if it prevented this in the future for you. It might.