FS9 Weird Window Mode Problem

Hello folks,I've been having this problem from day one and am just now deciding I need to address it. Here's the deal:If I run FS9 in full-screen mode, everything is fine. Period, end of story.If, however, I run FS9 in windowed mode, I have this annoying problem. If I pop up the GPS window, and I'm in any view OTHER THAN the 2d panel, I get this "thumping" sound. It sounds like the sim is stuttering, even though the video display isn't stuttering and my framerates generally stay steady. If I get rid of the GPS display, the thumping goes away.I have a Dell 4550 PC with a P4 2.4 ghz processor and 1 gig RAM (333 mhz). I have a Nvidia 5600 256 meg video card, but I only have the built-in sound card that came with the PC.My solution has been to run FS9 in full-screen mode, and I guess I can live with it, but I like to run other programs at the same time and it would be nice to be able to run in windowed mode as well.Thanks in advance for any help!Mark