Strange tapping sound from rear when engine off

[Dauphin]

Hi everyone,

Lately I've been driving around with the heater on low since it's been so frosty lately. All weekend whenever I parked the car and switched off the engine, there was a muffled tapping sound coming from the rear of the Fairlane. I opened the boot and didn't find a person or gremlin and it sounds like it's coming from inside the chassis or framework.

I thought it was just because of the heater's more-than-usual usage and something was "stretching" or "constricting" inside the cabin.

But last night it happened again when I had not used the heater but this time quite a bit louder than before and I got under the car. It sounds like it's something to do with the fuel tank but I'm not registering any increased fuel usage and there's no raw petrol smell or leaks underneath.

Has anyone encountered this tapping sound before in the rear, when they shut off the engine?

Thanks,

Andrew.