slow exchange backup

[kevinNNI]

My exchange mail backup's typically run at 100 or so MB/min, but occasionally (maybe one a week, no pattern) they will drop down to < 40 MB/min. on my network graphs i noticed a large ammount of traffic going to a remote location. the traffic turned out to be my exchange server making a ton of LDAP queries to an off site AD server. (if you want the ethereal sniff, i can email it to you). i'm convinced this is why the backup runs slow, but I dont know what would cause it to query in the first place (there is an AD server for this facility, it doesnt make sense why it would use an off site one)

i'm using w2k server sp3, e2k sp3, veritas 8.6. the tape is directly connected to the exchange server.

Thanks!