The Stig's secret subterranean lair is the perfect place to make a lot of noise with a lot of noisy cars. Welcome to Top Gear Tunnel Run. In the fifth episode of our series, our tame racing driver welcomes the Mercedes S600 limo... Wait, what?! Fear not, because while the W140-era Merc S-class is famously quiet (it even had double-glazed windows, so you could hear a pin drop in the cabin) it also had the same V12 that powered the original Pagani Zonda. And thanks to a trick exhaust, this one sounds like an old Formula One car.