Causes for pump vibration?

That could very well be it. The impeller is the only moving part, it rides on a little ceramic bead.

If one of the vanes isn't plugged up it may be the little metal seat in the bottom of the impeller that the bead goes into. If thats getting a little worn (the metal seat) it could make it whine. Maybe try a tiny bit of hi temp white lithium grease and see if it stops it. I know on a couple of the Laing pumps there has been a little bit of some blackish grease on the bearing when I opened them up, I mean a real tiny amount..

This is a old DDC, the D-5 is about the same, the pump inlet is just orientated differently, just pull the impeller straight out, its just the magnetism of the coils holding it in.

Sharp rig you have there, looks good!

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This was the one other concern I was eluding to but figured the turbulence would purge it. I am betting that is what it is. If you look at the pic you can see that my res is directly above the pump. The way the water flows into it causes a churning and some bubble formation. I am of the mind that over time the fine aeration has made it into the pump and I bet it has collected. Servicing it will be a pain but I think I can do it without having to tear it apart too much. I'll also top off the res so that the return doesn't cascade into it and cause the aeration. Hopefully that will do it. Thanks guys!

DigitalBear...thanks. It was going to be my case mod entry in the last contest we had but some stuff didn't show up in time and a few things caused me some trouble so I had to pull out.

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Like a passive rad but with the fans blowing across the tubing it cools it down... I think.

Maybe the pump trapt air inside?

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how meaning performance wise, i should have been more specific.

and doubtful about the air seeing his orientation of the pump

Well, I took the pump out and opened it up...nothing to be seen as far as crud. I tried running it for a couple seconds dry (yeah, I know you're not supposed to but they can handle a few seconds) and the vibration was still there to the same degree as it was originally. I noticed the small lead weights (this one has 3...maybe I'll snap a pic later) and using a small jewelers screwdriver to check they all seem tight.

Long story short ending, I scavenged from my last rig that I'm not running anymore...same pump but with the Laing sticker instead of Swiftech. It has been sitting dormant for about 3 months. Took it out, hooked it up, added more water and started her up...silent as always. If I hold it you can still feel a little something but it isn't enough to cause noise. We'll see if this changes over time. Doing this though now makes it official that my last rig is no longer going to be used so I have to decide what to do about/with it...an old AMD 3200 with a BFG 6800 AGP video card and 2GB of ram. Decisions decisions.

About the homemade rad/heat exchanger...doesn't work too badly. I'm not out to push this thing so I am only running 3.6 right now (no power increases needed) and it is running right around 51-52C at the high end (folds 24/7). I don't think that's too shabby for what I got...uneven, non symmetrical coils that were hand bent around a 3" diameter x 6' long piece of PVC. The tube it's in only leaves about 1/4" gap per side clearance. I also added a center tube to ensure the airflow went over the coils and not into the middle and then back out at the last coil. That one has mabye 3/4" clearance to the coils. It is basically the diameter as the center hub of the fans.