Popping in left front speaker w/Engine running

[dlbrown]

I have an '02 Ultra with premium sound. About a month ago on a long trip home the left speaker developed a popping noise that increased in frequency as I accelerated, almost like it is picking up noise from the coil or plugs??? With the engine off, it sounds great, but after I fire it up it will pop and as I increase the throttle the popping increases. I changed plugs, didn't help. Removed the outer fairing to look for any bad connection, didn't find anything. I swapped both left and right speakers and the popping still happens on the left side, so I know the speaker is good. Both rear speakers and the right speaker sound fine.
Any ideas???
Thanks in advance

[Serg06]

Check the wires going to the speakers.