98 Contour Starting Problems

I have a 1998 Ford Contour SE with the 2.5L V6. Awhile back I had to replace the alternator and found the ground on the engine was bad. Fixed that. Recently the charging system light was flickering but I thought it might have been a speaker/amplifier system that was installed so I removed the wiring to the battery for that. No light flickering now but I tried to start it the other day in the blistering cold (16F or so) and it just made this whiring sound. I had lights and electric locks but it whirred at me. No ignition sounds like it was trying to start or clicking like the battery was too weak. I had a buddy jump me and it started right up. Got home shut it off and tried to start it and it worked.

Next day for work it would not start. Had the battery tested - said it was just a bit low. Had it charged. Still have that whirring problem and cannot get the vehicle started. Not sure what the next move to make should be. Any ideas?

sounds like your battery is shot.