I would have to suspect the same thing WiLL does...u kno cuz subs are at a lower frequency so it's kinda odd having engine whine coming from them. What else do you have hooked up. Driving lights or anything. Does the whine come on stronger at night when your headlights are on?
But yea...I wouldn't say 9 times out of 10 is the ground, unless u recently changed your battery or had an alternator check. But grounding would be the first thing to look at.
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