My m4600 recently started a continuous beep after power up. Here is the sequence:

Turn power on, screen flashes quick text display, followed by the normal win 7 pro boot screen. When boot screen shows a continuous beep runs for about 30 seconds to a minute followed by normal boot sequence. After logon is complete, the computer appears to run ok.  If I power down and immediately power back up the process is the same.

Any ideas as to what this is and how to fix it?

Computer is the M4600 with windows 7 pro 64 bit. All updates are in and drivers up to date as checked by the support assist. Device manager shows 1 device with no drivers but that has been the case for a couple years. I have not been able to nail down what the device is but it has not affected my use of the computer.