How to create EMI/EMC noise for testing product behavior in noise environment?
Ask the lab what they use and buy one for yourself, keep in mind test equipment is expensive. A better thing to do is use proper grounding and shielding practices. 

If the EMI is conducted (through the supply of the device, then you should be able to use line filters, ferrites and capacitors to block the transients from coming in on the supply. 

If the EMI is radiating, then use proper shielding to block the radiated emissions from reaching the device.

I suspect you have a ground loop and an improper ground or ground loop. Split grounds are one of the quickest ways to have trouble in a design. It is important to control ground currents in any design and where they end up, this is best accomplished through proper layout. 

Get the book Electromagnetic Compatibility Engineering by Henery Ott. It is a really good resource.