Okay, I suspect that the really only sensible, reasonable, not-insane thing to do is to buy a new car, but I don't have the money for that, so I'm just trying to find out what the worst that can happen is...
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2001 Nissan Altima: 146,000 miles on it.
I recently got in an accident which messed up the front end of my car. The bumper had to be replaced. I drove myself from the scene of the accident to the body shop and at the time didn't hear any sounds with the engine -- the car seemed fine "except" for the bumper being gone and the frame behind the bumper being damaged. The radiator, behind the frame, did not seem to be touched, and that, combined with driving the car home for the accident uneventfully, was enough to make me decide to keep the car instead of scrapping it. (When I say "except" in the previous sentence, bear in mind that I understand the car was for all intents in purposes totaled. It's just that I need a car to keep getting paychecks in order to pay rent, I can't afford a new car, and I had only had liability insurance. Because it will likely be ruled my fault, I'm kinda screwed.)
I got the car back from the mechanic, and now I hear a high-pitched humming noise when I turn either right or left. This is particularly noticeable at low speeds (5-10 mph); at normal driving speeds (30-40mph, say) I don't hear it, or maybe only baaaarely hear it. I haven't yet taken it on the freeway.
I'm afraid there's something very much wrong with the axle or differential or something (be aware that I know more-or-less nothing about cars, and I'm already basically just spouting jargon that is meaningless to me).
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What's the least that could be wrong? What's the most-likely to be wrong? What's the worst that could be wrong?