Help! Iphone 3gs speaker not work when recieving after 4.3.3 Jailbreak & Unlock

[Rubbish@Tech]

Hello if anyone can help it would be great I'll try and explain as clear as poss:

Problem: iphone 3gs - the speaker does not work when receiving calls

software 4.3.3 and is running on baseband: 16.15.00

I had to upgrade the baseband to 16.15.00 to unlock it .

I jailbroke using Redsn0w 0.9.6rc16, it downloaded Cydia and the 16.15.00 baseband.

I went into Cydia and used Ultrasn0w to unlock it, need it unlocked as using other simcard.

All seemed to work fine except speaker not working when recieving calls, which seems very odd to me, do you think its a software issue with the baseband, is there anything I can do? I've heard its possible to downgrade somehow but no idea how.

Also I'm using a mac btw, Any thoughts as it can't be a hardware problem as it worked prior to jailbreak.

Many thanks for looking,

Laura