When my oil furnace starts up I'm hearing a whistle like sound coming from the oil tank. The noise continues until the furnace stops. It seems to coming from the fill gage area.
The furnace runs OK just has this annoying sound. Could there be a blockage in the vent system?
Thanks

Vent/air sucking sound will cause a noise. The vent should have been piped outside when installed to help prevent this. It could also be the oil pump singing through the lines. Usually this is a indicator of a failing oil pump.

Loosen the vent to see if the sound is eliminated.

hvac1000
I removed the vent cap(which is outside) and the sound remains. I used a 3ft hose to listen along the line,filter and the pump and the origin maybe the pump. Which is 15' from the tank.
Thanks