Airbag system would not emit any noise. The noise should be from something else, most likely related to vacuum and it couls be anything from the brake power booster to HVAC system.
The cost of repair for the SRS would depend on what is at fault. If you let me know the EXACT trouble code for the SRS indicating, I might be able to get more information on it.
Wednesday, January 12th, 2011 AT 2:21 PM