Sounds like a restricted exhaust sound by your description. Have you noticed a lack of performance while driving since this noise started? Another possibility is a vaccum leak under the hood but rare on acceleration. Check that the tailpipe is not restricted. Visually look under the car for damage to the exhaust. (I don't know if you're in a snowy area, which could be snow plugging the pipe also.) If appears OK, it's possible the Catalytic Converter is plugged.
Acura Legend was created in 1986.
There is no such thing as a 1998 Acura Legend. They were last produced in 1995. After 1995 Acura began making RLs instead of Legends. Perhaps you mean 1998 RL?
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