AVR-Chat

I am using a Atmega16 running at 7.37Mhz.  

I am also using a LCDPlus. I talk to it with the Rs232 Hardware UART. 
It has a ULN2803A with 8 relay Darlington Drivers. This also includes 
blocking diodes. I am using 5v Relays with contacts rated at 250v 10a.

The setup uses a momentary button to interrupt on Int0. The relays 
energise Mains contactors 120v 1a and ring a bell 120v .6a.
The system works fine with no load on the relay contacts. 

When I connect the contactor and bell I get false interrupts. I can 
software out the problem by disable/enable Int0 before and after the 
relay call. But I would like to fix it.

What I have done:
Use 1 supply for relays and 1 for the AVR.
Adding a power line filter before the power supplies.
I used a car battery and a dc to ac inverter to Isolate the unit from 
the contactor power.

So far no real fix.
Any Ideas??

JoeT