Hi Burt,
I just gave it a listen and those are some great vocals, is that you singing? Very nice!
I agree, there are definitely some problems with the frequencies, especially in the mid-high to high end. So much so, in fact, that it was almost painful at times listening at a moderate level through my monitors. The highs were really too much for me. I don't know if you have anything applied to the overall mix in terms of EQ, compression, etc, but I'd maybe start there and strip some things out to see if you can tame those highs. I'd also take a look at the guitar tracks, because it seemed to me that a lot of the bite and high pressure was coming from the guitars, which are pretty constant throughout the song. Not to beat a dead horse, but the cymbals and high hats were the same. I'd roll off some of the highs on those to make it less biting. Oh, and one more thing, if you are using effects on many or all of the tracks, check your tone controls in the effects settings and roll off some highs, or at the very least, make sure you aren't emphasizing the high frequencies in your reverbs, delays, etc.
The only other thing I'd recommend is to do some panning away from the center. Spread those guitars out to give your vocals some space!
For what it's worth, I've been using soundclick.com for several months and I don't notice much change, if any, in the way my music sounds streaming from that site than when I'm listening to it directly from Logic on my Mac. Are you worried about the conversion to .mp3 or something about uploading it to their site and the way they play it back?
Best Regards,
Dave DeWhitt