Had a party on Sat night with the Vista's playing med to high levels continuously for about 3 hours when all a sudden there was a very loud popping noise on one of the speakers. I immediately turned off everything, wait a little bit, turned it back on and everything is back to normal. This actually happened before on my old SL3's during another party also. Is this normal for ML speakers? My pre is Emotiva UMC-1 and amps are Emotiva XPA-1's. When it happened on the SL3's, I had the Emotiva XPA-2 amp.