DCC SOUND SPEAKER PROBLEM

[darticus]

Today I was running the trains and one train with sound hit a rough section of track and the sound started cutting on and off. Than it stayed off. Took the train tender apart and couldn't find any unhooked wires. I couldn't get the sound back on. Than I did something and the sound started going on and off. Thinking it was a wire problem I tried to move all wires and keep the remaining wires still. but I couldn't find the problem it just kept going on and off. I let the speaker fall an inch to the table and the sound came on. By taping the speaker the sound started going on and off. Finally the sound stayed on after hitting the speaker on the table. What could cause a speaker to do this and did anyone ever find this to happen. This is an N scale train so real small stuff. Ron