Any problems with H/E Pump?

[KCCobra03]

The other day after my car was warm, shut off for 20-30 min. then re-started it made a horrible noise like a bearing was going out. I jumped out, and narrowed it down to the H/Exchanger pump in the front corner. It had the whole car vibrating. The coolant wasn't at this point circulating at all. I drove it about a 1.5 miles and it stopped and at this time the coolant was circulating. Any thought as to why? Is it going out you think? I have had it happen before but didn't know from what or why. The car never overheated and it didn't rev up with engine rev. Anyway just curious.