If you are on windows 8 or 10 I’m not sure of any fixes to this. Basically, at the end of the day, finding an old XP computer to play on is probably your best bet. If this is windows 7 maybe try putting your visual settings to performance.
I’ve run into this on my windows 7 machine. Make sure your ClearType settings are set to off. Also, if you have a browser window open while launching rm in windowed mode it will cause thi sometimes as well.