Hi! I've played quite a few Hullahs; nice instruments. What sort of a bridge does it have? It sounds like a common problem with stringed instruments; the 'pull' of the strings over time raises a bulge behind the bridge. This used to be a big job, but there is now a quick and cheap cure; a thing called a 'bridge doctor' produced by Stewart MacDonald luthier supplies in the USA. I've just repaired the same fault in my Rob Armstrong mandocello using this gadget, and it really does work. Link here . PM me if you want more info, but it sounds like this might do the trick. Until then, think about lighter strings or dropping the tuning a little. Hope this helps.
Tim