HEADTEACHER Sandra Norgate couldn't quite put her finger on it and then she realised - the low-level humming from her infant pupils was mimicking the screeching tyres from the nearby Silverstone race circuit.
It was a hot summer's day, all the school windows were open and at the world-famous track up the road, drivers and mechanics were testing the tyres in preparation for the Grand Prix.
"It was really funny," said Mrs Norgate. "The children were completely unfazed, they were just getting on with their work but they were humming in tune to the noise."
This weekend as visitors flock to Northamptonshire for the biggest Formula One fixture in the British motor-racing calendar, the two village schools will be running their own money-spinning event.
While villagers open up their homes in lucrative bed and breakfast deals, the playgrounds at the infants and junior schools in Silverstone have become much sought-after car parks.
The schools, which between them have just 159 children, sell space at pound;10 a day, netting them between pound;500 and pound;1,000 each over the three-day event.
"It's a good little fundraiser," said Mrs Norgate, whose school for four to seven-year-olds also has bucket collections among race-goers.
"It's great," said Peter Chivers, head of Silverstone junior. "It's money from outside the village and means that we're not always having to ask our own parents for money.
"A lot of people who have parked here before, ring up and ask if we're doing it again."
But as always, there is a downside. Heavy traffic clogging up the roads means staff often have to leave home at least half an hour earlier than usual. Pupils resort to bicycles or walk.
And then there's the inevitable litter. "We always have Operation Spring Clean after the Grand Prix," said Mr Chivers.