Motorola Droid :: Inconsistent Sd Card Mounting Via Usb

I have the latest Motorola drivers on two different laptops, but sometimes my SD fails to mount on the PC when I plug it into the USB. I am able to mount most of the time and do normal file operations, no problem. But sometimes I go into failure mode where no matter what I try the SD won't mount. I try rebooting the phone and laptop, trying my other laptop, uninstalling an app I suspect is causing a problem, but probably isn't, etc. Then, sometime later, for no apparent reason, I'll plug the phone into the laptop and suddenly it's working again. I see threads about SD mounting difficulties, but none that address an intermittent problem like I'm having. Any ideas about diagnostics, fixes, or preventive measures?

When it fails to mount, the symptom is that with many attempts, the phone will make the mounting sound repeatedly, but never mounts. Other times, it makes the sound once, as if it succeeded, but it doesn't mount. I've checked the log with aLogcat, but I see nothing that I can tell might be informative, but then I'm not an expert with that stuff.

I must say, the error is really vexing. Mounting works well enough to use the SD card for transferring files, but then just when you need it (to transfer something back) it fails.