I drive a chevrolet cobalt 2006 LS sedan. Experiencing hard vibration at idle and braking while 'air con' is tunred "on". Have checked forums for similar experiences, other chev cobalt owners state this is normal. I'm wondering if I may need to get my 'air con' serviced, or go with what other owners are stating? Also experience hard vibrations when my stereo is on at high volumes, dont know whether i may have to ditch my subs and amplifier/ service my 'air con'?...Do I have a problem or is it normal?