Hey, I own a 2009 Toyota Corolla with about 100,000 miles on it....I do some serious driving to and from work, particularly in the summer. Recently I've begun to hear a humming/rumbling/growling sound whenever I go above 30 mph. The sound disappears when I go slower or idle. The sound remains if I coast in neutral downhill (so I don't think its an exhaust leak or muffler problem). I suspect the sound may be coming from the left front wheel bearing - but obviously need to take it to a mechanic and have it on a lift to know for sure. How long is it safe to go before getting this fixed? Funds are tight right now and I'd rather wait until I get my tax refund. Is it something I can put off a bit or does it need to be addressed, particularly in winter weather?