Waking up to 4″ of snow yesterday, I went down to start, clear and warm up the car.

Inside I could hear a regular “knock knock knock” – almost as if one of the tappets was going, but much bigger. When I revved, it didn’t increase in pitch or rate.

Outside the car I couldn’t really hear it, and once the engine was up to temperature, it stopped. I haven’t heard it since.

Any ideas what it could be/have been? My only thought is something somewhere having frozen up and that vibrating.

Heater fan….

cryptic….. and what would be the problem with it to make that kind of noise? And more importantly, how much to fix when it goes kaput?

Did you have lots of electrical stuff on? Heated screens, lights?
Our Focuses alternator complains with a similar noise when it’s loaded up with a cold start and lots of electrical drain. It soon dies away.

no lights, heater yes. Not heated windscreen (i normally remember that about 2 minutes after setting off).

Trapped baby robin trying to escape until it was incinerated to death ? 🙁

Checked all fluid levels?

Sticking valve?

Is the noise coming from the glove box? I had a knocking sound (intermittent) from the glove box and it was the heater fan. (V common problem on mk 1 foci )

Replaced the fan and resistor pack for about 45 notes[list]

Can’t be the alternator if the noise didn’t increase with revs.

Hang on my Puma did this.

It was the heater control valve.

Bought one off ebay and fitted myself.

Google heater control valve issue.

Try running the heater on full hot for 10mins then full cold.

Is the air filter newish?

Either way I bet its a new hgv.