Congestion at SBC/AADS NAP?

Has anyone seen what may be ATM level congestion at the Chicago NAP recently? ...or have you seen it in the recent past? We're having trouble pinpointing a problem, which may have been occurring for a long time, but just now really beginning to affect us significantly. We are seeing latency on certain peer sessions go through the roof (often more so in one direction than the other) and cannot (at least not yet) attribute it to hardware/link issues or problems with our edge device. Thanks for any insight, John