LG U400 Sound issues

Got a LG U400 on three and was wondering if any one else has had sound
issues. It will play a sound alert for a text message and then the
slide sound does not function. If i however then play some music on it
the slide sound works again. Sometimes also if it rings it does the
same thing and the other sound that stops to work is the one where you
are pressing the keys and it creates a sound for every press.

I have phoned three they sent me a new one but it has the same problem
was wondering if anyone out there either has same problem or has a
resolution

Neo