Audioprism Mantissa tube preamp buzz

Hello everybody, I've just re-tubed this preamp and after hooking everything back up I have a loud buzzing coming from the speakers. I tried a different amp and putting the old tubes back in but I still have the buzz. I've narrowed it down to preamp being the source of the problem. This piece also has an outboard power supply. Is there anything that I might try to fix the problem or should I just take it to a tech. I appreciate any suggestions. THANKS