So one night i parked my car and the next morning it was dead. It cranked like a half then 1/4 then nothing barely enough for lights on dash. I boosted it and it fired right up ran fine. Turned it off. After 1 min fired right up again. Went to Safeway came out fired right up. Came home left it for about 3-4 hours dead. Boosted it again fired right up. Went to Canadian tire for new battery came out fired right up. Each time when the car is off i can hear a buzzing or groaning sound coming from the battery area but im sure its not coming from the battery its self. The alternator is brand new and its charging over 15v never had any dimming lights on dash or headlights. Now that i hooked up the new battery it made the sound soon as i hooked it up so i left it unhooked to prevent drain if there was any. The next morning i went out and hooked it up there was no sound but after about 3 min it started like ... . .. ............ then stopped again. Sound is only there when car is off and it has been cold out. We had a few days of -40 then it has been +3 up till this problem.
Ive talked to a few people and they said it could be the regulator but i searched it up and there was no light issues nor indicators of that and there was a small amount of corrosion on the neg post but i cleaned that off completely before i removed the old battery. Now my issue is was it the old battery? Pretty new id say a year or 2 or is its this odd buzzing that i don't remember ever hearing before? I dont have the money to replace the mysterious part if that's the cause so i dont wanna take it in right away and i was gonna borrow a voltmeter and such in the next few days to do further testing. Any input from experience or otherwise appreciated.