loud screeching noise while talking

[JandH]

i am a Senior lady and barely know all the settings on my Blackberry Curve 9330.  I mainly use it to talk on, but thought i have all the basic settings done. 

I was talking on Christmas Day to someone when a loud screeching noise kept happening (only on my end).  I later found out it was because someone was trying to call me while i was on the phone talking and they left voice mail, and/or had texted me as well. 

It sounds like some kind of a screeching alarm screaming to tell me i have another caller trying to get me?  I would like to find a setting to turn that screaming sound off so i do not have that happen again when i am talking to someone.  I do not use Call Waiting and i do not put people on hold (as i do not know how anyway)

Please reply asap so i do not have this happen again.

thank you, J