Open the file in a good editor like vi and you will see all the nonsense characters and whitespace.
If you find the offending character and it is present many of your files you could probably use grep/xargs/sed to replace it out of all the files at once. Not sure how you do that on Windows though.
As to the answer suggesting that you leave off the closing ?> php tag... I've seen/heard this suggested several times but it just doesn't sit right with me. If you are going to omit the closing php tag from all of your files then you should put a comment at the end of every file indicating this so you know the file hasn't been truncated.
// end of file
However, if you are going to do this to all of your files you might as well just delete the whitespace after ?> tag. It's really not that hard unless you are sloppy with your coding.