I was driving home this evening and my electrical stuff shut down, more important my car began to make a humming sound. It was like an ooo sound. So I went and got a new battery and even then My car was still humming.
Ps. I gave my friend a jump this weekend and kept the wires on for about 5 minutes. Could I have fried my alternator or was it just that my battery was done for? Is the humming just the tensioner? Any suggestions will be highly appreciated.Thanks

 

The presence of the sound would tell you it isn't the battery... probably the alternator... You can get a Voltmeter (on any handheld multimeter) and see if the alternator is charging at the proper voltage...

A charged battery with engine off is about 12.2 to 12.4V

With the engine running... 12.4 to 14.6V is normal, leaning toward 14.4V... If the alternator is overcharging, it will destroy your new battery... Have it checked fast...