How to find the secret cars

How to find the hidden cars:

Rocket car:
The rocket car is hidden in the cargo bay in side a red open container on the left side of the bay.

Motorcycle:
The motorcycle is hidden in a shed filled with hay on the side of the left cow field.

Hamster ball:
To get the Hamster ball head ball to the lab and go to the shrinking mashing then after your shrunk you go and push the button behind the boxes then reset. After that go back to the fan and it'll be turned off go into the vents and the hamster balls will be there.

Limo:
To get the limo you first must go to the wobbly TV and go to the quiz (second floor) go to the hosts room and knock down the poster. Click the button to unlock the third floor then go back to the elevator and go up one more floor. Go to the present and once you get it you will unlock the limo.

UFO:
To get the UFO you need to go to the wobbly labs on top of the mountain then gather the parts to repair it.

1. get into the fork lift then move the colored crate piles and and put them in the squares that match after that jump across them and grab the battery.

2. Find the fuse which requires a lab coat in order to get that you must first find all the missing people in the lab room you mite as well grab the keys while your at it there in the room to next to one of the missing people after you put ion the lab coat you can enter the scientist only zone then take the first right and then to elevator where you will then be on a balcony and fallow the path the the fuse.

3. To get the fuel you must go too the formula maker up the stairs and put in the recipe corn, emerald, and purple potion.

4. to get the keys you must go back to the lab room and you should of already seen them go to the place where the last wobbly is and the keys will be right next to him.

Caveman car:
To get the caveman car you need to collect and turn in all of the following artifacts( includes there location).

1. To get the wheel you must go to the go kart race track and go to the trampolines on the hill the third trampoline up they'll be an X under it dig the up and you'll get the wheel then turn it in.

2. To get the pizza go to the pawn shop and keep on buying maps until you get it then turn it in.

3. To get the fossilized present go to the farm island and it is hidden in side one of the hay bails to get it out ram them until it pops out.

4. To get the spear go to the pawn shop in the city and get a hard map until you get it then turn it in.

5. To get possibly hardest one (it took me around 18 hours) the club you need to head over to the jungle island and go to the pirates and keep on doing the treasure hunting job until you get the club then carefully turn it in.

I hope this help you find the hidden cars when more come out I'll update this guide.
(Thank you dt405gt for telling me how to get the limo!)