Wiring a studio ---- lift all line level grounds at patchbay????

I have a client who is experiencing mild ground loop-style hum with a piece of gear I built for him.  It is dead quiet in my facility (a Neve-style, class-A circuit) but in his room it outputs a soft hum. 

I am tremendously familiar with the quirks of Neve-style class-A circuits with regards to proper grounding for hum and noise performance.  Like I say, it is dead stinking quiet in my facility, but in his it produces a soft hum, even with nothing physically connected to the inputs of the unit.

I'm thinking it is the wiring of his facility -- all of the line level I/O of his outboard gear have the audio ground pin lifted at the patch bay with the theory being that this will eliminate all ground loops between connected gear, but I'm not familiar with this practice.  I am familiar with the usefulness of lifting a ground at one end of a connection when a ground loop does occur, but as a standard interconnection philosophy to lift all grounds of line level connections at the patchbay??  My studio's patchbay has all ground pins terminated, so when I connect two pieces of gear via a patch cable, their grounds are connected as well.  I have no ground loop issues.

My question is this:  is his wiring method valid as a standard, across-the-board method for connecting balanced audio gear?  If so, I have somehow missed out on this in my career so far.  He apparently paid someone a lot of money to wire his studio up, and this was the method the guy recommended and claims lots of folks use.  I guess I haven't paid significant attention to such issues (shame on me?), but I just haven't had issues with things connected together, except for the very rare, odd occasion.  I would think this isn't standard, given the fact that many pieces of gear don't actually connect audio ground and chassis ground/earth directly.  As such, it seems to me that by not connecting ground pins between pieces of gear you have different pieces of gear with different ground potential.  Isn't this asking for problems?

I'd love to help him determine the cause of the hum, but really need to know a little more about the approach to wiring that his facility uses, and its potential drawbacks.  I apologize for such a lengthy post.  Any information you guys could share would be helpful to me.

Thoughts??

Thanks!!

I have done it all ways.  The laziest is to lift all shields at the bay!  The best compromise is to tie all at the bay and lift at all equipment connections except mic pres with P48 and other select boxes that want to be tied.  The "true theory" was to always lift shields at the load side, which did not lend well to equipment changes.

The practice is correct, but done backwards IMHO.  Traditionally the patchbay was part og a huge piece of metal chassis holding the "console".  It was a "gravity thang" and it was best to have all noise flow to ground via the biggest metal mass.  Many bays had all shields bused together at the bay like SSL, Amek, Harrison, Trident.  Neve liked separation so wiring the outboard would follow the console.  Today there are fewer consoles, so you have to look to the biggest mass, and most often it is the wiring itself so the bay gets all shields tied and bussed.  The few hummy boxes are delt with on an individual basis.

If this guy's room is wired lifted at the bay, console or not, the rules should follow.  Maybe yours is a piece that likes to be shield tied at both ends, which is more of a personality thing than anything bad, so he needs to tie shields at his bay- the real reason why you do not lift all of them at the bay because it is a PITA to tie some of them once the bay is wired!  Usually they are cut, so you have to go in and extract a little piece of shield etc.

You/he can verify this by interfacing your equipment with simple turnarounds to the bay and finding the best config to make it quiet. 
Mike

This is my first go to spot for grounding.
http://www.jensen-transformers.com/an/generic%20seminar.pdf
It tells how to trouble shoot.  How to test and produce good gear, including the "Pin one problem" and how to test for it.
On top of all the good info, there is a great list of references at the end.

Frank

What kind of gear is it? If it's a Neve style mic pre and he has it sitting on something with a big power transformer in it, you could be getting hum coupling into the input transformer.  It would be more of a pure 60hz (or 50, depending on where you are)  type of hum, not a buzzy type of thing. Just a thought.

Yes it could be the power the unit is being fed at this guys shop. Possibly at your shop you have a nice power conditioner and maybe  he doesn't?
    My very hummble .02cents. I've found some gear likes to have its ground lifted and some doesn't. at the patchbay  i've made up some TRS cables with the ground cut - to patch in different equipment....its actually been a headache deciding how to wire up my patch-bay. but after lifting all the grounds and then reconnecting them all, I decided to leave the grounds connected as it is much easier to life the ground via a cable then connect it later...like was mentioned before..
I think most of my problems come from my wacky console....but it just something to work with I guess

I've wired some big studio's in the past and I've never lifted the shields at patchbay side (actually, I wouldn't lift grounds anywhere near outboard equipment)
You can't have any ground loops since the shields to and from the patch are only connected at one side, through your unit into safety ground, which is the only (dirty) ground connection between the equipment.
What (console?) is he connecting it to? Does this problem occur if it's connected to other outboard equipment? To and from the patchbays or even directly.

Thanks for the feedback.  It gives me much to think about.

BTW, he's monitoring through a pair of stereo monitor inputs (balanced) on a Digidesign ICON.  I'll have him connect it to other things and see if the noise persists.

Thx.

try isolating the case from the rack rails (if he has the unit in a rack with other units),  just take it out of the rack to test and see if the unit is still has "noise" when the chassis is isolated from everything

try plugging the unit in grounded (bypass the ground lifts of the patchbay)

try a ground lift plug on the AC line to see if the noise is louder or quieter (just a test, don't ground lift AC lines on gear permanently, it's dangerous!)

double check the wiring of the studio lines to/from the patchbay, never know what's going on until you test for yourself