Kind of a spin off of Striders post and Jess's comment

[Thunderbolt]

Do you have a story about a vehicle and it having a weird noise or problem that was hard to diagnose?  A guy that I worked with said that a car he had bought had this strange noise that happened especially when his gas tank was low.  Turned out someone had put a soft drink can in the tank when it was made.  Only discovered when the tank was removed and shaken.

[Jess from VA]

Spent a day in a car with terrible noise in it.

Mother in law.

This particular diagnosis was easy. 

Pulled my stock exhaust interstate slowly up my drive and hear a clicking.

Looked all over and found nothing.  Pushed it down to my shed and it reappeared.

Little stones in the tire tread.

[Hooter]

I'll bite. Friend of mine had a new GTO. Every time he turned it clunked in what we thought to be the right rear. Finally after climbing under this thing, in the trunk a half dozen times, I rode in the back seat. He made a couple of turns and the clunk was coming from the panel next to the seat. We went back to his house and I took the panel off.

There hanging from a string was a small bottle with a note in it. It said: "glad you found this, did it make you nuts"? Your friendly GM worker.

[..]

Pebble stuck between disc and brake pad.

[John Schmidt]

I put some marbles in the gas tank of an old girlfriend's new boyfriend. Drove them both nuts. The best part of it....he asked me if I could fix it for him, he not knowing what it was. The dude couldn't change a light bulb without an instruction sheet. Told him I wouldn't do it for nothing so he gave $100 plus parts. In the end I told him I had to pull the tank and replace it with a good used one, didn't tell him the good used one was his own. Best job I ever had as a teenager, one Saturday afternoon and I made $100. I then asked the old galfriend out, just to see what she'd say. Said yes, so we went to the drive-in movie. 

[..]

Working as a driving instructor one of my co workers hid a kipper in my car. it took me 2 days to find it.

My revenge was to put crushed mothballs down the windshield vents. He had to take the whole dash out to remove the pieces.

[Savago]

@John: remember me to never buy a bike from you.
 

[Crackerborn]

I had a Dodge Tradesman van that I worked out of for a number of years. After work one afternoon I was supposed to go to the folks house and mow the lawn while they were out of town. All the way to their house I kept hearing a strange yowling kind of noise. When I got there and shut the van off the noise stopped for a moment then got really loud as I walked around the front of the van. I looked over and in the front air vent under the windshield there is a little orange kitten looking back at me. It took the rest of the afternoon to take the air grill off and coax the little begger out of the air ducts. How it got there will remain a mystery.

[Steel cowboy]

Back in 1980 I took my F-150 van and a 4 wheel drive GMC three door suburban and converted the van to a 4x4. The suburban had floating axel diff's and a separate transfer case fed by a jack shaft, so I could use the ford engine and trany but add the GMC's diff's and transfer case.
 I took it in at a local shop for new tires to finish of the build I had them put 36 in tires on my rims. As soon as I pulled away the van could not be driven above 30 mph with out it shaking violently. The shop told me it was the tires I brought them, were bad and I should of purchased the tires from them. I brought it back to my house and a friend helped me pull a tire off, we found old tire weights in side put there by some one at the shop. All four tires had weights in them.
My response to the shop and his helpers (all of them friends of each other) was to shove potatoes in all the car's exhaust pipes and moth balls in their tanks. I did it only to the cars they were fixing to resell. I denied everything to the police when they came to my house and never heard from them again, but did drive by, honking the horn every time I passed in front of the shop.
I did purchased a locking gas cap. Lol

[Jess from VA]

Good story.   

Esp. since the statute of limitations has long run.   

What goes around, comes around.

[MAD6Gun]

 Where do I start. As a GM tech for over 30 years I have seen a lot of sabotaged vehicles. A washer tied to a string behind the glove box on a pontiac Minivan that hit the dash braces on turns. A beer bottle in a 87 Chevy truck door. One guy told me of a caddy Eldorado that had a marble welded into the rocker panel. Would roll forward and back when the car accelerated and stopped. rocker had to be opened up to get marble out. Heard another of a bottle in a dash with a note in it that said "rattled like hell didnt it". That is just a few..

 Although for the last ten years or so I had not heard or seen any sabotaged vehicles. In my opinion. With the new systems of vehicle manufacturing using  computers to monitor all stages of assembly it would make it much easier to FIND the person that "installed" the offendng material.

[Savago]

With all this stories of American made sabotaged vehicles straight from the factory line, it is no wonder that Japanese manufacturers claimed the USA market.

[BobB]

I had a Dodge Tradesman van that I worked out of for a number of years. After work one afternoon I was supposed to go to the folks house and mow the lawn while they were out of town. All the way to their house I kept hearing a strange yowling kind of noise. When I got there and shut the van off the noise stopped for a moment then got really loud as I walked around the front of the van. I looked over and in the front air vent under the windshield there is a little orange kitten looking back at me. It took the rest of the afternoon to take the air grill off and coax the little begger out of the air ducts. How it got there will remain a mystery.

In cold weather, the farm cats would at times jump up into a warm engine compartment.  On several occasions, one of them would go through all nine lives when we started the vehicle...

[bill-jr]

I had a Dodge Tradesman van that I worked out of for a number of years. After work one afternoon I was supposed to go to the folks house and mow the lawn while they were out of town. All the way to their house I kept hearing a strange yowling kind of noise. When I got there and shut the van off the noise stopped for a moment then got really loud as I walked around the front of the van. I looked over and in the front air vent under the windshield there is a little orange kitten looking back at me. It took the rest of the afternoon to take the air grill off and coax the little begger out of the air ducts. How it got there will remain a mystery.

In cold weather, the farm cats would at times jump up into a warm engine compartment.  On several occasions, one of them would go through all nine lives when we started the vehicle...

Now that offends me ..

[MarkT]

Did you see this?  Victory Vision with a squeak.  Watch to the end...

https://www.youtube.com/watch?v=ir6tw7K78bc

[Hooter]

 First...   second...

[Jess from VA]

It's a long walk home baby.

[FryeVRCCDS0067]

I'm sure some have heard this before but riding home from work one afternoon my bike was making a strange sound above about 50 mph which would go away as I slowed down. It took several times of riding, stopping, inspecting, and riding again before I shut off the motor and realized the sound was coming from some 1/4" washers in my shirt pocket banging together in the wind.

[Farside]

Did you see this?  Victory Vision with a squeak.  Watch to the end...

https://www.youtube.com/watch?v=ir6tw7K78bc

  

[BudMan]

I'm sure some have heard this before but riding home from work one afternoon my bike was making a strange sound above about 50 mph which would go away as I slowed down. It took several times of riding, stopping, inspecting, and riding again before I shut off the motor and realized the sound was coming from some 1/4" washers in my shirt pocket banging together in the wind.

That sounds like something I would do!