DCC Sound/Speaker Problem - Model Railroader Magazine

Hey everyone, I am hoping you can help me with a problem I am having.  This week I installed my first ever Soundtraxx Tsunami decoder into a locomotive and at first things went well, now I am having an issue.  Here is my setup:

Atlas GP40 Locomotive

Soundtraxx Tsunami  TSU-AT1000 EMD 645 Decoder

QSI Speaker

I hardwired everything and everything worked beautifully, I had lighting control, speed & direction control, and all the sounds and it sounded great!  The only problem was i accidentally put the decoder in the wrong way so the directions were backwards.

I took the decoder out and flipped it around reinstalled everything put it on the track and at first the speaker started working like normal making the engine startup sound and then it kind of shorted out and stopped working.  Lighting still works, moves forward fine, but when I put it in reverse I get a lot of humming and distortion thru the speaker.  It still moves in reverse fine but weird distortion thru the speaker, and the sound functions no longer work.  I tried reversing the polarity of the speaker wires and this did nothing.

I took the speaker our altogether and the lighting and forward/reverse worked great.  Tried putting the speaker back in and forward works fine, but when I put it in reverse it starts buzzing again thru the speaker.

Anyone have any idea what is going on?  And why does this happen only in reverse?  The only thing I can think of is when I was soldering the wires back onto the speaker my soldering iron accidentally touched the back of the speaker and may have melted it a little.  It seems like the speaker has shorted out but why does it only buzz when I put it in reverse?

Any help would be greatly appreciated!