Do they make a quiet great sounding phono pre amp??

I don't want to argue with Raul too much, because I do agree that a solid state phono stage has a better chance to be really dead quiet with very low output MCs (let's define that as 0.3mV and below), but it is also possible to get there with tubes and especially with hybrid devices employing both transistors and tubes in the signal path.  Typically in the latter case, a transistor is used at the input as voltage amplifier.  Apparently the Herron using its MC input is one such device.  With MM or MI cartridges, any really good tube phono stage ought to be very quiet; if it's not, there's a problem either with the design or the tubes or with grounding.  My vintage Quicksilver full function preamplifier, old as it is, is as quiet as any CDP, when driven either by my Grace Ruby or my Acutex LPM320.

Raul, You've stimulated me to take my Klyne 6LX out of mothballs and give it a listen on my Beveridge speakers.  I built a mega-oversize outboard PS for it, and Stan Klyne massaged the phono section only a few years ago.  The only difference between a 6LX and a 7 is the balanced output option on the latter, which I would prefer if it were available.  However, the 6LX is indeed dead quiet. When last I did listen to its phono section, I found it just a little "dry" sounding, compared, of course, to tubes. After that, I ran a Silvaweld SWH550 tube phono stage into the Klyne, feeding the Bevs. That was a great combo.

Matt, You really ought to take one or both of your troublesome phono stages to the home of an audiophile friend or to a local dealer, and listen to them on a completely different system.  That way, you may figure out that the problem lies downstream from the phono stage, which very well could be the case.  Likewise, you might borrow a known good working phono stage from a friend or dealer and see how that goes in your system.

That said, I have to agree with you that the fact you are having no problems with digital sources is puzzling.  For a shot in the dark, you might check out what is going on with the interconnect cables you use between the phono stages and your linestage.  Swap in some completely different cables, and try switching to a different pair of input jacks on your linestage; you may have a bad solder joint somewhere on the linestage side. Also, check whether said cables are passing near a source of EMI or RFI.  

Further, if all else fails, based on the rave review of it by Michael Fremer, which I just read on-line, you might consider the iFi iPhono2 for only $499.  You can tell when Fremer REALLY likes something, and I think that is the case with this unit.

Pursuant to checking out the Klyne 6LX, I did install it into my Beveridge system last night and listen to it for about 2 hours.  It had been completely out of service for many months, so it took a while to "bloom", but when it did, the sound was excellent, as Raul predicted.  It has the expected virtues of solid state: very low noise (actually no audible noise at all, even between tracks of an LP with stylus in groove), very good clean bass response, very good articulation of separate instruments.  Plus it had virtues of good tube gear: huge sound stage, very good sense of depth, good retrieval of decay.  Compared to the best tube phono I have heard on this system, there was a very teeny tiny slight bit of dry-ness.  Not offensive, just different.  But the trade-off was in favor of the virtues.

Another way to deal with the ground loop without resorting to cheater plugs is to use a full wave bridge rectifier installed between chassis ground and audio ground, in either your preamp or phono stage, or both.  You install it such that the diodes provide the isolation between the two, but there is only a ~2V voltage drop (that of two diodes in series) between audio and earth ground, which ain't going to hurt anyone.  You would need an experienced tech, unless you understand the theory. A simpler method is to use a low value resistance, like 100 ohms, to separate the two grounds, which might or might not work.  Meantime, like Almarg, I don't think the danger of what you have done is so great as to cause panic.  The un-grounded components are in contact with earth ground via the ICs, assuming that your amplifier's earth ground and audio ground are in continuity.  OR, even simpler, you might find that re-arranging the plugs so that they all come off the same AC receptacle would permit you to go back to using 3 prongs. 

I vote keep what you have, now that you have solved the problem.  Manley Chinook is excellent in and of itself.

Nandric, How can you, the consummate logician, pose such a question, since likely no one of us has heard both pieces?