I am in a related boat..... I get a "soapy" taste from centennial if I use a bunch of it. When I brewed northern brewer's Dead Ringer..... I really noticed it - ton of Centennial though. I am fine with about 2 ounces, but as soon as I hit 3-4-5-6 ounces of centennial, it gives me a soapy/cleaner type flavor..... So, I could see that with Cascade as well, as they are similar hops in some ways. I like cascade and centennial... I just blend them in with other hops like chinook, columbus, Pearle, falconers flight, simcoe, etc...
Now, that being said, you want to make sure it is really something you are getting from the hops..... and not "soapy" from some other source in your process. Cascade is a great hop, maybe "the" hop for pale ales and IPA's over the last couple decades. So, just be sure to look into other variables and possibilities.