Hi all. Noticed driving home today a whine like a noisy fuel pump whine. Went on for about 150km. Then intermittent. When i got home and locked vehicle it did it again for a few seconds. Then when I unlocked it it was going off for ages. I then locked the vehicle and it stopped. When i opened up the back it was coming from the sub box. I know about the issues with water ingress and part of my inspection i checked thoroughly for evidence of moisture in the side compartment and it was fine. All the electronics work fine and the sub is clear and doesn't distort at normal levels. (Haven't cranked it up yet). So I'm not sure what the issue is there are there any electronics/ sound system engineers in the house?

TIA

Jc