[V8] A8 emissions problems

[Jason Wilkerson]

Guys,
  I know this is the v8 forum but I have come to realize you all are a wealth of info on audis in general.  I have an issue with my 1999 A8.  The CEL came on the other day.  Two codes - 
 
    16839/P0455 - Evap system, large leak
    16825/P0441 - Evap system, incorrect flow, intermittant.
 
I have checked the following:
 
     Purge valve, pulled vac on the engine side, no leaks.  Tested electrical operation, works fine.  Tested on car and it modulates like it should - OK
 
    Fuel expansion tank for leaks, visually and with pressure - OK
 
    Fuel cap and neck - OK.
 
    Fuel tank lid with seals for sender and fuel pump - OK.
 
    Carbon canister under spare tire - OK.
 
    Evap test pump - Not sure?
 
Here is the run down:
 
    Before the CEL illuminated, I was hearing a 'whining' sound coming from the pass rear wheel.  Turns out it is some sort of check valve in the expansion tank above that wheel.  I don't think this is the problem, but just a symptom.
 
    Not sure if it is relevant, but before I started to hear the 'whining' and before the CEL, I backed into a building.  It was not hard and really didn't even put a mark on the car, but - it would seem that it was about the same time that this happened and the same time that it currently takes to reset the CEL.
 
    I pressure checked the whole fuel system last night and found nothing leaking.
 
    I'm leaning toward the evap test pump - I may have to buy one anyway because I broke one of the fittings off trying to remove it to look for anything obvious.
 
SO - any suggestions?  I am at a loss.  Thanks in advance.