The Plainridge Racecourse and town officials  are alerting residents that the track  has begun construction on a parking garage, which requires some drilling and blasting  at the site over the next few weeks. Blasting is taking place Monday through Friday  from 9 to 10 a.m.  On blasting days, there will be three audible warnings: three whistles  five minutes before the blast, two whistles  one minute before, and one whistle  once the blast is complete. For more information, visit the town's website, www.plainville.ma.us.