Repairing a PSR-E433?

[SciNote]

I am pretty convinced that there is something wrong with my PSR-E433.  A while back, I posted about some distortion that occurs using the reverb.  Now, I am noticing some distortion with certain sounds or combinations of sounds.  It's a sound that almost sounds like a blown or loose speaker under certain conditions, but it is not a blown/loose speaker, because the sound is also audible through an external amp and speakers.  It doesn't happen all the time or on all sounds, but I don't remember hearing this distortion before.  It mainly occurs right at the beginning of certain sounds, such as a loudly played piano sound (when I say "loudly played", I mean striking the key hard, as to make the sound louder).  It also seems like the higher-pitched harmonics of certain sounds, like synth-strings and '80's brass when combined using split or dual voice, seem to interact in a way that sounds distorted -- also something I never noticed before.

So, my question is, has anyone ever had their keyboard serviced or repaired?  I would really prefer not to replace the keyboard, and I am wondering if anyone has had any good or bad experiences with getting a PSR-E-series keyboard repaired.  I tried to call Yamaha today to see if they could recommend a service and repair center near me, but I couldn't get a hold of anyone in the amount of time that I had, as I was on break at work.