Moaning sound from drysump oil lines 308

Hello from Germany,

I would be curious, what your thoughts or theories are regarding a phenomenon I have in my drysump lubrication circuit since I have installed new, custom made oil lines last year.
Each time I start my car it makes a moaning sound definitely coming from the lower suction line on the oil tank. Only audible - but then evidently - from the driver's seat and while holding one ear into the drysump oil tank. My theory is, that the new teflon lines transmit the gear noises from the oil pump via the oil line to the tank, which acts as a 'soundbox'. Investigating with my stethoscope confirms all this. It seems that the old rubber lines were damping the noise transition while teflon does have much less dampening capabilities.
O.k.; this is my theory and the dampening thing is confirmed by technical literature. But what keeps me thinking is the fact, that the noise disappears after approx. half a minute. Why does it disappear ? And - more mysterious - why does it also occur with the engine oil thoroughly warm after a short engine stop ?
Do any of you have any further theories ?

Best Regards and thank you in advance

Martin