I have a very similar problem with rapid, loud, continuous beeps while Win7 is booting on a Dell Latitude D620 laptop ever since it was upgraded from 1GB to 4GB of RAM. These are not POST beeps. Beeps only occur after POST while the Win7 boot manager is loading drivers, before the login screen appears. Also, they only occur when BIOS is set for "Quick Boot", which in fact is very quick (less than a minute). I have the latest available Dell BIOS (Ver. A10, released 5/19/2008).
The oddest thing is that if I shutdown the laptop and reboot within 5-10 minutes, the beeps never occur! However, if the laptop is off for about 15 minutes or longer, the beeps always reappear as long as I set the BCD store to bypass the Windows Boot Manager screen. If the BCD store is not set to bypass the Windows Boot Manager screen, then the WBM screen appears (requiring the return key to be hit) and the beeps follow on half or more of the delayed boots.
Win7 itself runs fine. No missing icons. All hardware tests pass. No stuck keys as far as I can tell. Memory is recognized as expected.
Very annoying and from a safety perspective I hesitate to turn off the windows beeps entirely using device manager. I have searched the web intensely and see no other references to this behavior. Is there an issue with Win7 buffer overflow on "Quick Boot" with 4GB RAM?