Skimmer issues

I have a reef octopus skimmer and it currently sounds like a washing machine mid cycle with alternating wooshes.  I have noticed that when I pinch the air intake line the noise goes away and the skimmer is very quiet.  Obviously with no air input the skimmer doesn't do anything, but I was hoping someone might have an idea of what I can do to try to fix the problem.  I've looked up countless videos of the reef octopus skimmers and while some of them are louder, it is always a constant volume, not a woosh woosh sound that mine is currently making.
Any help or troubleshooting steps are appreciated!

 

It is the Reef Octopus DNWB 110. It is not producing any skimmate that I am aware of, and the bubble production seems to be low from what I have seen from others online. I will try to get some video of it tonight on my phone and post it to youtube so you can see/hear exactly what I am referring to. I don't know what a muffler on the air line would be, so I can't answer that question directly. This is my first non-nano sized skimmer, so I am shooting in the dark myself in reference to exactly how to utilize it correctly. The water exiting makes a normal splashing noise, and that is definitely not the noise in question. Again, I'll try to post a video, but it really sounds a lot like a washing machine that is alternating back and forth in the cleaning cycle.

 

So after watching it some more it appears that water is going into the venturi tube where the tube meets the pump and it goes in and out in time with the noise I am hearing.

Here is a video of it I just took. http://www.youtube.com/watch?v=TQ8Crj6LoWw&feature=youtube_gdata_player

Around 14 seconds in you can kinda see the water popping in and out of the tube. Around 36 seconds I pinch the line and the sound goes away. Throughout it all I think you can hear the chug/whoosh sound I am trying (although probably ineptly) to explain. Let me know if you need any more info or want video of something else!

 

Thanks for all the suggestions, this has already proven more fruitful than my countless hours of google searches. I messed with the air tube some and the sound has lessened considerably, but it is still present. I don't really care about the sound (my wife does but that is her problem), I just want it to work properly.

MXC207 - does your skimmer produce much skimmate? Mine has yet to but I have only had it hooked up for about 3 days.

Danmgray - I bought it from a fellow reefer, so it is new to me but it is not a new skimmer. No matter where I pinch the tube the sound completely stops and the skimmer runs nearly silent, and the sound has been there since the first time I plugged it in. But again it isn't new so I don't know if it has always done so. The previous owner has not responded to my emails asking about it yet.

Foo - I'll be honest and say I am not sure what the volute hole is. I did some quick looking and I think it is the port where the air enters the pump via the tube, not the port at the other end of the tube...but I have been wrong in the past. If so, do I just take the pump apart and make sure everything is clean? Is that a good idea anyways since this isn't a new protein skimmer? He said he cleaned it, but I can see how missing a small part can happen, I know it is happened to me in the past with other equipment.

 

That is roughly what I thought you meant, but it is nice to have it clarified. I had already resolved to take the pump apart and soak it in vinegar for a bit this weekend to see if that was a problem. Also if a hose is old and pretty pliable, could that also contribute to the issue? I am seeing the hose as easy to squeeze, so it compresses slightly instead of remaining firm and allowing enough air to pass through it. The hose itself is attached to the pump intake and then on the other end at a built in silencer. There is a little slack in the hose so it could be shortened slightly, but not a lot.

 

Mine is the wedge pipe version. I have run it with both the outlet submerged and not submerged and there is no change that I can see. That being said I have it unsubmerged because that is how it is recommended to be used. The top tube of the wedge is the non-siphon bar as far as I am aware. I don't know how I would check to make sure it is working properly. I do know that if I turn it to raise the water level high enough it eventually starts to suck water down the venturi hose instead of air, but I don't run it that high. Also I unhooked the tube from the non-siphon bar/silencer last night to see what that would do, and you could hear it trying to suck air into the pump with the same sound in the video but much louder.

My first steps this weekend will be a vinegar soaking and to replace the tubing, and if that doesn't work I may call their support line to see if they have any ideas.

 

I took it apart and soaked it in vinegar because it had some calcium built up inside. I also took some Q-tips and scraped out a ton of gunk from inside the pump. When I hooked it back up the sound is completely gone and it is running well so far.

Quick question, before I did this all I had a major overflow from the skimmer on Friday. The venturi tube was sucking in water to the pump instead of air. I assume this is because a vacuum of some sort was created; is this likely because the air input was clogged up? Or is there something else I should check? I can't take another mistake with this tank or the wife will end me...

 

Okay, hopefully cleaning it out will prevent more overflows. Thanks for all the help!