http://jen3ral.wordpress.com/2010/03/11/disable-the-annoying-beeps-your-computer-makes-even-with-sounds-muted/

I don't normally even have my sound turned on while computing, so I have no clue how long this has happened (how many releases)

When I close a folder it beeps.  Cute little "beep" like I might hear if there is a message waiting on my phone. It seems to happen no matter which folder is closed. I checked Windows sounds and it says "no sounds" and I cannot get the same response outside of the program anyway.  Nope, not using New Mail sound either - it's turned off. The help file only talks about New Mail sound - it doesn't mention any "folder close" sound.

Pegasus Mail for Microsoft Windows
Copyright (C) 1992-2011, David Harris, all rights reserved
Electronic mail to support@pmail.gen.nz.

WinPMail version: Version 4.63 (Win32), Dec 22 2011, build ID 325
Language resources: Standard UK English resource set
Extension Manager version: 1.14
Operating mode: Standalone
User name and ID: Liz, 0
Windows version: 6.1
Windows flag word: 0
WINPMAIL.EXE directory: F:\PMAIL\Programs
Home mailbox location: F:\PMAIL\MAIL\Liz
New mailbox location: F:\PMAIL\MAIL\Liz
TMP environment variable: C:\Users\Liz\AppData\Local\Temp
TEMP environment variable: C:\Users\Liz\AppData\Local\Temp
LAN-based SMTP support: N, N, N
NetWare MHS support: N, N, N
Built-in TCP/IP support: Enabled
  - WINSOCK version: WinSock 2.0
  - WINSOCK path: C:\Windows\system32\WSOCK32.DLL
Commandline: -I Liz
Active -Z options: 32768
PMR variable: (None)
PML variable: (None)
MAI variable: (None)
NB variable: (None)
Autofiltering folders: 29 (29 active, 0 inactive)
Last new mail count: 0
Message size soft limit: 0 bytes
Message size hard limit: 0 bytes
Attachment size soft limit: 0 bytes
Attachment size hard limit: 0 bytes
 

The sound is probably coming from the OS not Pmail. Try turning off windows "beep".

All Windows sounds are completely turned off, all other applications, including most TSR ones (anyone remember that term?) I turned off. When the laptop sound is off, then the sound does not happen. I doubt that it is a system sound. If there is even a Windows setting that would make a sound, a hint would be nice. As of today, none of the other windowed type programs or any other make the same noise.  I'm not necessarily saying that PMail is the source of the code for the sound, it just has the action that triggers it. I have tried to duplicate in and have checked all of the sound sources that I know about in Windows. I'm simply looking for some more ideas.