if it sounds like a bearing noise and it isn't, and increase's in noise as speed rise's, then it's probably your tyres. put your 15" ones back on and check. my old tyres did this. changed rubber,no noise.
cbl's shouldn't make any differentence, you'd put them in if the steering wheel's shaking at speed.
So you only use spigot rings if you get steering shake?! What about the extra strain on the studs? For the sake of a few quid, buy them.