my 98 is o0ut of warranty so his is likely to as we close the books on 2002.

THe pop sounds like the shifting of something. The reason it isn't doing it until you drive again for a while it that is isn't moving quickly but gradually. Could be a suspension piece like an A arm or shock but could also be a caliper bolt that is loose. If you are mechanically inclined got your ratchet and sockets out and tighten all bolts. If not take it somewhere and have it inspected.