Call Volume & Occasional "Mumble"

When I'm on a phone call, I have the volume buttons on the side of the device pushed all the way up to the maximum volume level. I'm still not getting the loudness I had on my previous blackberry. Is there an internal setting within the options somewhere also that may control this?

Also, have any of you experienced anybody you have been speaking with on the phone tell you occasionally you sound mumbled or it goes in and out?

I've had (2) people tell me this already! A bit concerned as although its a great gadget, it needs to be a PHONE first!

Thanks