If you've tried different bows, it's probably the rosin. Is there rosin buildup on the strings? Or are they squeaky-clean (aha! I wonder if that's the origin of that phrase?), meaning the rosin won't "take hold?" The suggestions about cracks or the little sleeves that are meant for the bridge slots aren't likely sources of a squeak, especially if you've tried a few pizzicato notes to make sure there's no harmonic resonance causing the sound. (By the way, a "wolf tone (or note)" isn't a squeak by any means -- it's a 'wooomph' or 'howl,' hence the 'wolf' in the name.)

A clean bow, with no finger-oil (one of the main reasons that rosin won't stick to bow-hair), and good hair on it, should be enough, even with "ordinary" rosin, without loading up the rosin till it makes a cloud about your head while playing. (I get a cloud around my head while playing, but that's just because my playing draws flies). The point someone made about good rosin is a good one, just like the amazing difference good strings makes. And the humidity can be a factor, for sure. If all else fails, try putting a humidifier in the case and leaving it a few days, to see if this changes the sound. If it does, then a case humidifier would be a good investment; if it doesn't, don't bother. Oh, I said to put one in before you buy one, didn't I? Well, a piece of sponge can be wetted down and placed in a baggy, with the top of the baggy open, as a quick-and-cheap humidifier; a proper one can be purchased if it proves useful.

Anyway, you've had several good suggestions here, so, good luck.

Songbob Clayton