W202 tapping in footwell

[goldenbadger]

Can anyone shed any light on a tapping in the drivers footwell of my 94' W202. The sound is very similar to on old cars through the speedo cable, it is also able to be felt through the brake pedal especially when at a standstill. I've read suggestions on the site of it being linked to the heater but doesn't alter at all when varying the fan/temperature - noise is every 3 or 4 seconds.

Thanks in advance

 

[type49]

Could be heater circulation pump. Open bonnet. OSF inner wing below exhaust manifold height but on the chassis rail area, you will see a motor with a pipe in & out @ 90 degree to each other. See if it's that.

 

[Myros]

could also be the resonance

of the duovalve opening and closing. Try it with the heating set fully cold, it should go, and the heating set fully hot, it should go. In between hot and cold, the duo valve opens and closes to maintain temp according to the feed from the temp sensor in the light assembly