Serial Read interfering with Tone

Hi all,

I have an Arduino Mini Pro 16 MHz which is reading bytes using the SoftwareSerial library Read command from a RS232 port via a Max232 converter. I'm also trying to use Tone to generate a series of different notes. Both sections of code work perfectly when tested on there own. When combined and running together the serial read still works perfectly, but the tone generated is completely corrupted. It appears that the interrupts from Read and Tone are colliding. I've tried swapping the output pin to the piezo speaker so that Tone using a different clock/interrupt to no avail. Does anyone no of a way around this problem? If not do I need to use an Arduino which has additional hardware serial ports such as the Mega?