Have you ever wondered just what makes your car hum?

You could always take a peek under the hood, but here in Alabama, you can go further than that.

The state's three auto assembly plants offer public tours of their operations, a popular ticket for everyone from students to retirees.

Inside the vast factories, you'll get an up-close look of the industry's inner workings as sedans, SUVs, minivans and pickups are built from the ground up.

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Tour specifics vary by plant, and some areas of the operations are off-limits. But all are thorough, lasting at least an hour.

At Honda in Talladega County and Hyundai in Montgomery, the free tours are by reservation only and they're filling up fast this spring.

Hyundai gives tours on Mondays, Wednesdays and Fridays at 9:30 a.m., 12:30 p.m. and 2 p.m. and on Thursdays at 6:30 p.m. Children must be at least six years old.

Anyone can reserve a tour on

but there are few open slots in the coming months because of Spring Break and school groups.

Honda's tours, offered on Tuesdays and Thursdays at 9 a.m. and 1 p.m., also are booked well in advance. Go to

to schedule a tour; children must be at least 12 years old.

If you've got luxury taste, you'll have to wait a while for an inside look at the Tuscaloosa County operations of Mercedes-Benz.

Starting this week, the company's visitor center and museum is closed for a major renovation, and public plant tours are on hiatus.

The move comes as the plant prepares to launch new products, including the C-Class sedan this summer.

The visitor center and museum showcases the 128-year history of Mercedes, including the German automaker's 20 years in Alabama, with milestone vehicles and other memorabilia.

The company will reopen the visitor center and resume public plant tours later this summer. Check

for updates. Children must be at least 12 years old for a tour.

Mercedes plant tours cost $5 per person or $4 per person for groups of 10 or more.