Two days ago, I noticed a noise that seemed to come from the motor. It sounded like a "distant motorcycle hum" (best description I can think of); however, you wouldn't hear it unless you were paying attention. It started when I got my car to 40+ m.p.h. and stopped when I slowed down. Over the past two days, it has become slightly worse; just enough to where it's annoying now and happens almost all the time when I drive, regardless of speed. However, if I rev up the engine in Park, the noise doesn't happen. I took it to my uncle, who's a mechanic, and he says its most likely a wheel bearing. He drove it and heard the noise, but he said it wasn't "far gone" enough to figure out what side it was coming from. I had an 85-mile trip to make today, and when I returned, I could tell that it was definately coming from the driver's side. What do I need to do in the meantime? I have a short trip (~20 miles) to make tomorrow; is that going to be safe? They're getting replaced ASAP.