Underground noises

Julia has left a new comment on your post "LA to NY in 30 minutes": 

Yes we get a daily rumbling sound here in Bath, easiest to hear at night when everything else is quiet. 

It sounds like an underground generator. 

We also have a lottery funded Two Tunnels project, which sounds like Two Towers. It's a cycle path and due to open on Saturday with some sort of Opening Ceremony of course. The first tunnel is the longest cycle tunnel in Britain, don't know where the air vents are, but people died in there before when it was a railway, so that's encouraging. 

I went past the entrance today, it looks sort of industrial, with 5' high barbed wire fencing on either side of the tarmac'd road for quite a way. This is in a rural location. Trees have been hacked down. It looks like they don't want people to access the cycle path or leave it if they are on it, except by controlled access points. The tunnels themselves will be gated, sounds ominous.