air purging noise from fuel lines???

[melmount]

Sometimes when i turn the key on to allow the glow plugs to work and to let the fuel pump get going, I hear a whine of sorts. Like air blowing by the seal on the fuel filter cap. It does not do this every time, like maybe once every 20. I have noticed this mostly when warm. It seems to run well and is not causing an issue. It seems to be in the fuel filter area. No fuel is leaking. At least that I can tell. I am thinking it has to deal with fuel pressure cause thats when it does it, when its first pumping(engine off). I am thinking air is getting in and when the pump is turned on its pushing forcing the air to get out? Is this possible?
any ideas

[melmount]

If I decide to change all seals on the fuel bowl, I get the 4 fuel line sleeves and the O rings. Hows the bowl itself get attached down? does that part of the bowl need a gasket of some sort? I have air leaking somehow.