Bob Novella

Specifically, the expansion joint is made up of two or more metal plates, which overlap each other as the cars drive by or over the joint.

The joint flexes a little bit, which causes the plates to rub against each other and makes a squeaking noise.

Well, the previous guesser said it was the BART, you know, that BART transit.

No, that's not the correct thing, but someone did pick a very specific thing and I guess where they live.

So anyway, that is correct.

So let me play this for you again.

Yeah, and that's basically the expansion joint squeaking as the cars go over.

Absolutely.

Yeah, that gap allows, like, in the winter or the summer when the size of the bridge changes due to temperature, that expansion joint allows it to move.

And it's perfectly safe.

Oh, hell yeah.

Yeah.

I mean, if you didn't have them, the bridge would eventually break from the temperature changes.

Yep.

That's what I want to hear.

It's good.

That's a good thing.

All right.

I have a new noisy for this week.

This was sent in by a listener named Matt Tinnenberg.