Hello Nick,
 
I bought an Edirol UA-5 a few months ago and 
eventually returned it to the retailer (i took of that 30-day money back 
gaurantee because ultimately it wasn't the right product for my needs).  
Here's a breakdown of my experience with the interface:
 
1.  If I started PD with the -noresync flag, I 
could eliminate SOME of the clicking noises.
 
2.  I was never terribly successful using PD 
with ASIO with the Edirol interface.  the UA-5 could only support ASIO 
drivers on either the input OR the output.  So, If I stared PD with the 
-asio flag, then I had to also use either -nodac or -noadc.  That was a 
real drag.
(I don't know if the UA-1A supports simoultaneous 
INput and OUTput with the ASIO drivers.??)
 
3.  Ultimately, I returned the product and 
bought a MOTU 2408mkII.  It's about 2.5 times the price of the edirol 
unit..but I can use 24 input and output simoultaneously with ASIO --but on the 
downside, it doesn't have a mic pre-amp like the UA-5 had.
 
I don't know if this helps you at all and I 
understand that you're using the UA-1A which is different than the UA-5..but I 
thought I'd share my experience anyway.
 
Regards,
Dave S