Calls that are received in voicemail play normally on the Phone.
Those same messages that are then sent out via email gateway are distorted, it sounds over-driven like its too loud.
This is both on a 7100 and a 7200s running fairly current software. I have tried to adjust parameters and volume settings without effect.
Is this common? Does it happen on all systems? What about the SVMI 20i / 20e
Anybody else with this? Any cure?

When you look at the wav files properties, what is the bit rate for the file? Also if you look under email gateway in the mclass standard what is selected for message format of email at the bottom?

Windows shows Audio at 128kbps
I have tried both 8 bit and 16 Bit signed PCM in Mclass.

Is this happening from all mailboxes or just one mailbox?

It was only one mailbox user that complained but I was able to duplicate it on our Office system.
The problem seems to be in the message rerecording to email gateway, if the original message was too loud the email gateway message would be overdriven and distorted.
This was on SIP trunks. Calls from SIP to SIP were fine and translated OK. Calls from other sources (I called in via iphone) could be varying levels and would distort.
I have reduced Voip to SVMI in system wide volume to reduce the issue.