If I had to guess, I would say that the starter is not engaging the engine. When you turn the key to start, it energizes the starter and a solenoid that "pulls" the starter gear into the flywheel gear to turn the engine ovr. I suspect the roar is the starter motor turning and not engaging. You need to replace the solenoid, on some cars it is part of the starter and not available by itself.
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If I had to guess, I would say that the starter is not engaging the engine. When you turn the key to start, it energizes the starter and a solenoid that "pulls" the starter gear into the flywheel gear to turn the engine ovr. I suspect the roar is the starter motor turning and not engaging. You need to replace the solenoid, on some cars it is part of the starter and not available by itself.