I got a '04 1.4 Seat Cordoba here (340k on the odo!) and it makes a rythmic pulsating sound. The sound occurs under all conditions; warm/cold engine, low/high engine load etc.
At first I thought I had an exhaust leak, but it turns out it's someting with the crankcase ventilation. When I (cautiously)removed the oil cap at idling, the sound increased somewhat in volume, and the engine speed increased from 900 to 1000rpm. When I put back the oil cap, the sound stopped for a second, and then it continued again. The engine still pulls like a 75hp engine should. There's no check engine light on. (yes, that's a surprise for a VAG engine!)
These observations strongly suggest a leak somehwere in the crankcase, but there's still a considerable vacuum there. When I hold the oil cap near its seat, I feel that it's getting sucked back in place. The oil color is still good, there's no display of the infamous mayo on the oil cap or dipstick.
Could this be harmful for the engine? The older engines I normally work on have crankcase ventilation that just ventilates the crankcase vapours to the open air, so I suppose it's not that of a concern. The point is that I want to sell this thing, and such a sound naturally makes people suspicious of the engine's health status.
Any ideas or tips?