Euro Reef Skimmer - air tube noise

[lost_at_sea]

Hey all hoping to see if anybody has this same problem...

tank is newly established and very lightly stocked (90g + 30g sump) I have the RS-135 Euro Reef skimmer and seems to be starting to break in but the other day I noticed the air pipe that comes up from the motor has been making a 'slurping' sound quite frequently and it's becoming very loud and annoying...

has anybody had this experience?

[lost_at_sea]

so after another sleepless night I figured out that the issue was primarily to do with low water level (was running at 6inches, now up to that made a big difference in the frequency at which the slurping noise was made...

the second thing I noticed was it wasn't the actual airline tube that feeds the pump it was the open/close tube (1inch diameter) that is part of the skimmer that was making all the noise. 

I believe this noise is to be expected from some posts i've read online, so I created a DIY muffler out of ductape and a spare piece of PVC pipe. Seems to have helped quite a bit.