Originally Posted by Eurostyle
The air pump only comes on for short time at cold start up...No way near "especially after a bit of driving" like in his case...Not even mentioning the pump makes a loud sharp (sucking/compressor) noise, not ticking/knocking!
one can never tell; I've heard stranger things under an engine bay. the air pump is suppose to come on for a short time..but who really knows..it's obvious hes going to need a stethoscope to narrow down the potential area - needs investigating and shouldn't omit any possibility. process of elimination!!