Eshopps HOB psk100 noise

[SHADYreefer]

I purchased a Eshopps psk 100 HOB skimmer a month ago. It ran quiet at first, but now it has a loud noise. The noise is loud for 2 seconds than quiet for 1 second. I looked inside the pump and the piping. I can't find the problem!! The skimmer skims like normal.

[Guacamole]

Mine started to humm a bit and low and behold my lid was not seated correctly. Not sure if this is any help but just my experience. Love this skimmer