PacBell contact?

We're seeing some strange packet dropping behavior with a monitoring
host on PacBell DSL - if we send two packets back to back, the
probability that both get dropped is actually higher than the
probability of losing one packet if it's sent alone. We're trying
to explain the behavior to understand in what situations some of our
tools won't work, and I'd like to chat with someone in the know.

(PacBell's trouble@ address didn't seem like the right place).

Or, if anyone knows what kind of traffic shaping equipment or other
such would exhibit that behavior, I'd love to know. The only
places we've seen this are on DSL and Cable modem links.