Just wondering

I am no longer in the telecom biz but wonder if anyone knows how to explain
I was in charge of a Nortel network of over 100 PBX's connected through OC48
/ DS3 and T1's. There were ATM switches connecting the optical portions of
the networks. The site I am wondering about was main site>OC48>T1.
I had one campus that always popped up with a T1 error about every 2 to 6
days(sorry, over the years I don't remember the specific error code). It was
never enough to interrupt service but still it was a problem. I logged into
the NIU (don't tell Qwest) and didn't see any errors. I did a head-to-head
test with T-bird 2209's over the weekend many times and found the pipe to be
clean. I couldn't figure it out. I tried swapping out TMDI cards and even
swapped out CSU's with other CSU's that worked fine at other sites. Still, I
kept getting errors. I even had Qwest swap out cabnets and NIU's and my self
swapped out cables to the CSU and from the CSU to the OPT 11c. Still errors.
I tried different bonding grounds and different brands of CSU's, even tried
AC power to the CSU vs. DC. Still errors. I finally ran a cable directly
from the NIU to the OPT 11C (no CSU) and all the errors were gone for good.
I'm confused. What the hell is going on here? The CSU was configured the
same as all other sites and there were other OPT 11C's in the network by the
same install tech with the same configuration. We even set the thresholds
the same but still had errors only at this site. I even made sure that the
pairs were with in a couple of db (22 for one and 23 for the other) and feed
out of the same xboxes. TDR tests showed them to be the same. Qwest replaced
both doublers (only one per T1). The software RLSE was 23 at the main site
and 25 at the problem site. However, we had 3 other sites with RLSE 25 and
no problelms from them.
Like I said, I am no longer in charge of this site but as far as I
understand, they are still running directly from NIU to OPT 11c to keep from
getting the errors. Just a note, the customer was influentual enough to get
Nortel to listen to every word he had to say and he had a LOT to say if it
ment he could get some free service from us/Nortel. He got a computer log of
EVERY error that the switches spit out and always wanted us to explain every
one of them every day.

On another install job of over 20 Opt11c's (all through Passpost, back in
2004) we had a problem that some T1's would not come up or would come up
then go down. With T-birds we found the T1's to be OK most of the time but
the only way that we could keep a connection through the passports was if we
could get the Qwest tech to install a regen-NIU that keeps the db at 0. That
was towards the start of my career in telecom but, still I think of it today
and wonder why?

T1's seem simple in the text books but, seem to have strange errors that can
not be explained by logic when you get into the field.

I would love to here any comments about any part of this post.