The Car - '04 Audi A4 1.8 k04, Carbonio intake... and other james bond type stuff;-)

The Problem - Im getting a soft "hummmmmmm" under 20mph occationally. It doesnt happen all the time though, it seems to be coming from drivers side engine bay. Could it be line/filter running to boost gauge? I replaced the lines going from the t to the filter and to the filter to the gauge... still making noise. And I cant seem to make the noise happen at the dealer.. !!!! Seems also to be making it a bit more when the car is more on the warmer side.

What can it be guys...

 

more details on when it happens?
could be your vacuum supply pump next to your ABS module

 

Not sure of any more "details"... I mean... it happens under 20MPH and when the car has been driven and is warm/hot. It doesnt happen on any paticular gear or what not... just when driven under 20. any feedback would be awesome. thanks guys