To be honest pinkcowprint (cute name!) they wouldn't do much even if there WAS an address.
It must be horrible for you to hear that day in day out, absolutely heart-wrenching. No chance you could take a walk towards the noise and try to suss out where it is?
Unless the dog is hurt, or has no food, water or shelter, the RSPCA will do little. They will direct you to your local council's environmental health dept., to deal with the noise, but this doesn't really deal with the root problem. You'll be asked to fill out a noise diary. Do you know of anyone else who has heard the dog howl? If you are at no risk, it might be worth approaching the owners and mentioning it. Perhaps they aren't aware, although if the dog is being left for so long, perhaps they aren't suited to dog ownership anyway.
I hope something can be done.