>>> our final story here tonight, starts with a pretty familiar sound in cities and towns across this country. the rumble of the garbage truck up and down the street. on one particular street in fresno, california, that sound and the guy who drives the truck are making a difference in their own way in the life of a young boy living with autism. they're having a big impact as well on his family. we get the story to night from nbc's miguel almaguer.

>> reporter: 4-year-old greyson and his mom chrissy can hear the rumble they know he is on the way.

>> jumping up and down and flapping his hand and just feeling so much joy.

>> reporter: frank diaz looks forward to this stop all week.

>> i see joy. i see when he jumps up and down heap is excited.

>> reporter: like so many little boys , greyson loves the roar of the garbage truck .

>> hey, little buddy .

>> reporter: few know greyson struggles with autism making it difficult to communicate.

>> i didn't have a typical child who spoke or said mommy, i want to get out of bed.

>> reporter: a few weeks ago when frank pulled up greyson broke his silence.

>> he said "i want truck." it was a breakthrough into my world. and not only did he talk to me. he said three words.

>> reporter: for a family living with autism it was a milestone.

>> it is such a -- a rare but special moment between the two of us. honestly it was magical.

>> reporter: the kellies have two boys. little brother parker who is just 2, shows signs of autism, but is too young to be officially diagnosed. chrissy shares her family story on her blog, connecting with moms around the world.

>> you broke into his world when i couldn't.

>> reporter: greyson's dad michael says it is one man who is making a difference in their son's life.

>> frank gives me hope that people out there won't discriminate against my son.

>> i got your picture up there.

>> reporter: frank carries greyson's picture in his truck.

>> i saved all my breaks today.

>> reporter: a connection made with a few simple word, but with a meaning that goes so much deeper. miguel almaguer, nbc news, fresno, california.