Image copyright Reuters Image caption Mr Persic said there were around 200 walnuts hidden in the car

A couple in the US city of Pittsburgh found a surprise stash of hundreds of walnuts hidden under their car bonnet.

The nuts, along with a lot of grass, are believed to have been collected there by squirrels making preparations for winter.

Chris Persic posted photos of the car on Facebook warning that "rodents and vehicles do not mix".

Holly Persic only discovered the hoard when she was driving and noticed a burning smell and strange sound.

After looking under the bonnet, she found the stash, which the couple attempted to clear out before taking the car to a mechanic.

"Was absolutely nuts... no pun intended," Mr Persic said in his Facebook post.

Image copyright Reuters Image caption The original photo posted on Facebook, which got over 500 shares

"They were everywhere, under the battery, near the radiator fan," he told CNN. "The walnuts on the engine block were black and smelt like they were definitely roasting."

As autumn set in, walnuts started falling from the trees a few weeks ago meaning the squirrels must have worked quickly to build their hoard.

Although there was no damage to the car, Mr Persic warned others to check under their bonnets.

Image copyright Reuters Image caption Mr Persic said it took over an hour to clear out the car

Due to recent rain the grass under the bonnet was damp but if it had been drier it could have caught fire, he said, leading to far more drastic consequences.

"Long story short, if you park outside, do yourself a favour and check under the hood every once in a while," he said.